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“ROMANCE OF REALITY” SERIES 
Edited by Ellison Hawks 


ELECTRICITY 


VOLUMES ALREADY ISSUED 


3. THE AEROPLANE. 

By Grahame White and Harry PIarper. 

2 . THE MAN-OF-WAR. 

By Commander E. H. Currey, R.N. 

3. MODERN INVENTIONS. By V. E. Johnson, M.A. 

4. ELECTRICITY. By W. H. McCormick. 

5. ENGINEERING. By Gordon D. Knox. 



THE MARCONI TRANSATLANTIC WIRELESS STATION 
AT GLACE BAY, NOVA SCOTIA 



Drawing by Irene Sutcliffe 




























“ROMANCE OF REALITY” SERIES 


ELECTRICITY 

BY 

W. H. McGORMIGK 




NEW YORK 

FREDERICK A. STOKES COMPANY 

PUBLISHERS 











TKks 

. M3 




Gift 

Fuhl. ber 
APH 14 m' 



Printed in Great Britain 





\5 




PREFACE 

I GLADLY take this opportunity of acknowledging the generous 
assistance I have received in the preparation of this book. 

I am indebted to the following firms for much useful informa¬ 
tion regarding their various specialities:— 

Chloride Electrical Storage Co. Ltd.; General Electric Co. Ltd.; 
Union Electric Co. Ltd.; Automatic Electric Co., Chicago; Westing- 
house Cooper-Hewitt Co. Ltd.; Creed, Bille & Co. Ltd.; India 
Rubber, Gutta Percha, and Telegraph Works Co. Ltd.; W. Canning 
& Co.; C. H. F. Muller; Ozonair Ltd.; Universal Electric Supply 
Co., Manchester; and the Agricultural Electric Discharge Co. Ltd. 
For illustrations my thanks are due to:— 

Marconi’s Wireless Telegraph Co. Ltd.; Chloride Electrical 
Storage Co. Ltd.; Harry W. Cox & Co. Ltd.; C. H. F. Muller; 
W. Canning & Co.; Union Electric Co. Ltd.; Creed, Bill$ & Co. 
Ltd.; Ozonair Ltd.; Kodak Ltd.; C. A. Parsons & Co.; Lanca¬ 
shire Dynamo and Motor Co. Ltd.; Dick, Kerr & Co. Ltd.; 
Siemens Brothers Dynamo Works Ltd.; Vickers Ltd.; and 
Craven Brothers Ltd. 

Mr. Edward Maude and Mr. J. A. Robson have most kindly 
prepared for me a number of the diagrams, and I am indebted 
to Dr. Myer Coplans for particulars and a diagram of the heat- 
compensated salinometer. 

I acknowledge also many important suggestions from Miss 
E. C. Dudgeon on Electro-Culture, and from Mr. R. Baxter and 
Mr. G. Clark on Telegraphy and Telephony. 

Amongst the many books I have consulted I am indebted 


v 


Preface 

specially to Electricity in Modern Medicine , by Alfred C. Norman,, 
M.D.; Growing Crops and Plants by Electricity , by Miss E. C. 
Dudgeon; and Wireless Telegraphy (Cambridge Manuals), by 
Prof. C. L. Fortescue. I have derived great assistance also from 
the Wireless World. 

Finally, I have to thank Mr. Albert Innes, A.I.E.E., of Leeds,, 
for a number of most valuable suggestions, and for his kindness in 
reading through the proofs. 

W. H. McC. 


Leeds, 1915 


CONTENTS 


CHAPTER 

PAGE 

I. The Birth of the Science of Electricity . . x 

II. Electrical Machines and the Leyden Jar . . 9 

III. Electricity in the Atmosphere . . . . .18 

IV. The Electric Current . . . . # .27 

V. The Accumulator ...... 3 g 

VI. Magnets and Magnetism . . . . . -44 

VII. The Production of Magnetism by Electricity . . 56 

VIII. The Induction Coil ...... gi 

IX.L'The Dynamo and the Electric Motor . . . .66 

X. Electric Power Stations . . . . . -75 

XI. Electricity in Locomotion ...... 83 

XII. Electric Lighting . . . . . . .93 

XIII. Electric Heating ....... 109 

XIV. Electric Bells and Alarms . . . . .116 

XV. Electric Clocks . . . . . . .124 

XVI. The Telegraph ....... 128 

XVII. Submarine Telegraphy ...... 144 

XVIII.^he Telephone ....... 154 

XIX. Some Telegraphic and Telephonic Inventions . . 171 

XX. Wireless Telegraphy and Telephony—Principles and 

Apparatus ........ 179 

XXL Wireless Telegraphy—Practical Applications . . 203 

XXII. Electroplating and Electrotyping .... 213 

XXIII. Industrial Electrolysis ...... 224 

XXIV. The Rontgen Rays ....... 228 

XXV. Electricity in Medicine ...... 241 

XXVI. Ozone ......... 247 

XXVII. Electric Ignition ....... 253 

XXVIII. Electro-Culture ....... 258 

XXIX. Some Recent Applications of Electricity — An Electric 

Pipe Locator, etc. ...... 266 

XXX. Electricity in War ....... 274 

XXXI. What is Electricity? ...... 287 

Index ......... 295 

vii 








LIST OF PLATES 


Plate in Colour : The Marconi Transatlantic Wireless Station 

at Glace Bay, Nova Scotia ..... Frontispiece 

FACING PACK 

Hydro-Electric Power Station . . . . . . 30 

(а) Experiment to show Magnetic Induction . . . .48 

(б) Experiment to show the Production of Magnetism by an Electric 

Current ......... 48 

(a) Lines of Magnetic Force of Two Opposite Poles . . . 50 

(£) Lines of Magnetic Force of Two Similar Poles . . .50 

A Typical Dynamo and its Parts . . . . . .70 

Lots Road Electric Power Station, Chelsea . . . *76 

Power Station Battery of Accumulators . . . .80 

Electric Colliery Railway ....... 86 

Typical Electric Locomotives . . . . . .90 

Night Photographs, taken by the Light of the Arc Lamps . . 96 

Where Electrical Machinery is made . . . . .120 

Specimen of the Work of the Creed High-Speed Printing Telegraph 140 
Large Electric Travelling Crane at a Railway Works . . 164 

( а ) Marconi Operator Receiving a Message .... 188 

(б) Marconi Magnetic Detector ...... 188 

Rontgen Ray Photograph of British and Foreign Fountain Pens . 240 

Bachelet “Flying Train” and its Inventor .... 272 

( а ) Cavalry Portable Wireless Cart Set ..... 280 

(б) Aeroplane fitted with Wireless Telegraphy . . . 2 8o 


Vllt 



ELECTRICITY 


CHAPTER I 

THE BIRTH OF THE SCIENCE OF ELECTRICITY 

Although the science of electricity is of comparatively 
recent date, electricity itself has existed from the beginning 
of the world. There can be no doubt that man’s intro¬ 
duction to electricity was brought about through the 
medium of the thunderstorm, and from very early times 
come down to us records of the terror inspired by thunder 
and lightning, and of the ways in which the ancients tried 
to account for the phenomena. Even to-day, although we 
know what lightning is and how it is produced, a severe 
thunderstorm fills us with a certain amount of awe, if not 
fear ; and we can understand what a terrifying experience 
it must have been to the ancients, who had none of our 
knowledge. 

These early people had simple minds, and from our 
point of view they had little intelligence ; but they possessed 
a great deal of curiosity. They were just as anxious to 
explain things as we are, and so they were not content 
until they had invented an explanation of lightning and 
thunder. Their favourite way of accounting for anything 
they did not understand was to make up a sort of romance 
about it. They believed that the heavens were inhabited 
by various gods, who showed their pleasure or anger by 
A I 


Electricity 

signs, and so they naturally concluded that thunder was 
the voice of angry gods, and lightning the weapon with 
- which they struck down those who had displeased them. 
Prayers and sacrifices were therefore offered to the gods, in 
the hope of appeasing their wrath. 

Greek and Roman mythology contains many references 
to thunder and lightning. For instance, we read about 
the great god Zeus, who wielded thunder-bolts which had 
been forged in underground furnaces by the giant Cyclops. 
There was no doubt that the thunder-bolts were made in 
this way, because one only had to visit a volcano in order 
to see the smoke from the furnace, and hear the rumbling 
echo of the far-off hammering. Then we are told the 
tragic story of Phaeton, son of the Sun-god. This youth, 
like many others since his time, was daring and venture¬ 
some, and imagined that he could do things quite as well 
as his father. On one occasion he tried to drive his father s 
chariot, and, as might have been expected, it got beyond 
his control, and came dangerously near the Earth. The 
land was scorched, the oceans were dried up, and the whole 
Earth was threatened with utter destruction. In order to 
prevent such a frightful catastrophe, Jupiter, the mighty 
lord of the heavens, hurled a thunder-bolt at Phaeton, and 
struck him from the chariot into the river Po. A whole 
book could be written about these ancient legends con¬ 
cerning the thunderstorm, but, interesting as they are, they 
have no scientific value, and many centuries were to elapse 
before the real nature of lightning was understood. 

In order to trace the first glimmerings of electrical 
knowledge we must leave the thunderstorm and pass on to 
more trivial matters. On certain sea-coasts the ancients 
found a transparent yellow substance capable of taking a 
high polish, and much to be desired as an ornament; and 
about 600 years b.c. it was discovered that this substance, 


The Birth of the Science of Electricity 

when rubbed, gained the power of drawing to it bits of 
straw, feathers, and other light bodies. This discovery is 
generally credited to a Greek philosopher named Thales, 
94 I- 5^3 B - c *> an d it must be regarded as the first step 
towards the foundation of electrical science. The yellow 
substance was amber. We now know it to be simply a 
sort of fossilized resin, but the Greeks gave it a much more 
romantic origin. When Phaeton’s rashness brought him 
to an untimely end, his sorrowing sisters, the Heliades, 
were changed into poplar trees, and their tears into amber. 
Amongst the names given to the Sun-god was Alector, 
which means the shining one, and so the tears of the 
Heliades came to have the name Electron, or the shining 
thing. Unlike most of the old legends, this story of the 
fate of the Sun-maidens is of great importance to us, for 
from the word “electron” we get the name Electricity. 

Thales and his contemporaries seem to have made no 
serious attempts to explain the attraction of the rubbed 
amber, and indeed so little importance was attached to the 
discovery that it was completely forgotten. About 321 b.c. 
one Theophrastus found that a certain mineral called 
“ lyncurium ” gained attractive powers when rubbed, but 
again little attention was paid to the matter, and astonishing 
as it may seem, no further progress worth mention was 
made until towards the close of the sixteenth century, when 
Doctor Gilbert of Colchester began to experiment seriously. 
This man was born about 1543, and took his degree of 
doctor of medicine at Cambridge in 1569. He was very 
successful in his medical work, and became President of the 
College of Physicians, and later on physician to Queen 
Elizabeth. He had a true instinct for scientific research, 
and was not content to accept statements on the authority 
of others, but tested everything for himself. He found 
that sulphur, resin, sealing-wax, and many other substances 

3 


Electricity 

behaved like amber when rubbed, but he failed to get any 
results from certain other substances, such as the metals. 
He therefore called the former substances “electrics,” and 
the latter “ anelectrics,” or non-electrics. His researches 
were continued by other investigators, and from him dates 
the science of electricity. 

Leaving historical matters for the present, we will 
examine the curious power which is gained by substances 
as the result of rubbing. Amber is not always obtainable, 

and so we will use in its place a glass 
rod and a stick of sealing-wax. If the 
glass rod is rubbed briskly with a dry 
silk handkerchief, and then held close 
to a number of very small bits of paper, 
the bits are immediately drawn to the 
rod, and the same thing occurs if the 
stick of sealing-wax is substituted for 
the glass. This power of attraction is 
due to the presence of a small charge 
of electricity on the rubbed glass and 

/ . __sealing-wax, or in other words, the two 

Fig. i. —Suspended substances are said to be electrified, 
pith ball for showing gj ts p a p er are unsatisfactory for care- 

ful experimenting, and instead of them 
we will use the simple piece of apparatus shown in Fig. i. 
This consists of a ball of elder pith, suspended from a glass 
support by means of a silk thread. If now we repeat our 
experiments with the electrified glass or sealing-wax we 
find that the little ball is attracted in the same way as the 
bits of paper. But if we look carefully we shall notice that 
attraction is not the only effect, for as soon as the ball 
touches the electrified body it is driven away or repelled. 
Now let us suspend, by means of a thread, a glass rod 
which has been electrified by rubbing it with silk, and bring 









The Birth of the Science of Electricity 

near it in turn another silk-rubbed glass rod and a stick of 
sealing-wax rubbed with flannel. The two glass rods are 
found to repel one another, whereas the sealing-wax attracts 
the glass. If the experiment is repeated with a suspended 
stick of sealing-wax rubbed with flannel, the glass and the 
sealing-wax attract each other, but the two sticks of wax 
repel one another. Both glass and sealing-wax are 
electrified, as may be seen by bringing them near the pith 
ball, but there must be some difference between them as 
we get attraction in one case and repulsion in the other. 

The explanation is that the electric charges on the silk- 
rubbed glass and on the flannel-rubbed sealing-wax are of 
different kinds, the former being called positive, and the 
latter negative. Bodies with similar charges, such as the 
two glass rods, repel one another; while bodies with unlike 
charges, such as the glass and the sealing-wax, attract each 
other. We can now see why the pith ball was first 
attracted and then repelled. To start with, the ball was 
not electrified, and was attracted when the rubbed glass or 
sealing-wax was brought near it. When however the 
ball touched the electrified body it received a share of the 
latter’s electricity, and as similar charges repel one another, 
the ball was driven away. 

The kind of electricity produced depends not only on 
the substance rubbed, but also on the material used as the 
rubber. For instance, we can give glass a negative charge 
by rubbing it with flannel, and sealing-wax becomes 
positively charged when rubbed with silk. The important 
point to remember is that there are only two kinds of 
electricity, and that every substance electrified by rubbing 
is charged either positively, like the silk-rubbed glass, or 
negatively, like the flannel-rubbed sealing-wax. 

If we try to electrify a metal rod by holding it in the 
hand and rubbing it, we get no result, but if we fasten to 

5 


Electricity 

the metal a handle of glass, and hold it by this while 
rubbing, we find that it becomes electrified in the same way 
as the glass rod or the sealing-wax. Substances such as 
glass do not allow electricity to pass along them, so that in 
rubbing a glass rod the part rubbed becomes charged, and 
the electricity stays there, being unable to spread to the 
other parts of the rod. Substances such as metals allow 
electricity to pass easily, so that when a metal rod is 
rubbed electricity is produced, but it immediately spreads 
over the whole rod, reaches the hand, and escapes. If we 
wish the metal to retain its charge we must provide it with 
a handle of glass or of some other material which does not 
allow electricity to pass. Dr. Gilbert did not know this, 
and so he came to the conclusion that metals were non¬ 
electrics, or could not be electrified. 

Substances which allow electricity to pass freely are 
called conductors, and those which do not are called non¬ 
conductors ; while between the two extremes are many 
substances which are called partial conductors. It may be 
said here that no substance is quite perfect in either respect, 
for all conductors offer some resistance to the passage of 
electricity, while all non-conductors possess some conduct¬ 
ing power. Amongst conductors are metals, acids, water, 
and the human body ; cotton, linen, and paper are partial 
conductors; and air, resin, silk, glass, sealing-wax, and 
gutta-percha are non-conductors. When a conductor is 
guarded by a non-conductor so that its electricity cannot 
escape, it is said to be insulated, from Latin, insula , an 
island ; and non-conductors are also called “insulators.” 

So far we have mentioned only the electric charge 
produced on the substance rubbed, but the material used as 
rubber also becomes electrified. The two charges, however, 
are not alike, but one is always positive and the other 
negative. For instance, if glass is rubbed with silk, the 

6 


The Birth of the Science of Electricity 

glass receives a positive, and the silk a negative charge. 
It also can be shown that the two opposite charges are 
always equal in quantity. 

The two kinds of electricity are generally represented 
by the signs -f and —, the former standing for positive 
and the latter for negative electricity. 

The electricity produced by rubbing, or friction, is 
known as Static Electricity ; that is, electricity in a state of 
rest, as distinguished from electricity in motion, or current 
electricity. The word static is derived from a Greek word 
meaning to stand. At the same time it must be under¬ 
stood that this electricity of friction is at rest only in the 
sense that it is a prisoner, unable to move. When we 
produce a charge of static electricity on a glass rod, by 
rubbing it, the electricity would escape fast enough if it 
could. It has only two possible ways of escape, along the 
rod and through the air, and as both glass and air are non¬ 
conductors it is obliged to remain at rest where it was 
produced. On the other hand, as we have seen, the 
electricity produced by rubbing a metal rod which is not 
protected by an insulating handle escapes instantly, because 
the metal is a good conductor. 

When static electricity collects in sufficient quantities 
it discharges itself in the form of a bright spark, and we 
shall speak of these sparks in Chapter III. Static electricity 
is of no use for doing useful work, such as ringing bells or 
driving motors, and in fact, except for scientific purposes, 
it is more of a nuisance than a help. It collects almost 
everywhere, and its power of attraction makes it very 
troublesome at times. In the processes of textile manu¬ 
facture static electricity is produced in considerable 
quantities, and it makes its presence known by causing the 
threads to stick together in the most annoying fashion. In 
printing rooms too it plays pranks, making the sheets of 

7 


Electricity 

paper stick together so that the printing presses have to be 
stopped. 

Curiously enough, static electricity has been detected in 
the act of interfering with the work of its twin brother, 
current electricity. A little while ago it was noticed that 
the electric incandescent lamps in a certain building were 
lasting only a very short time, the filaments being found 
broken after comparatively little use. Investigations 
showed that the boy was in the habit of dusting the lamp 
globes with a feather duster. The friction set up in this 
way produced charges of electricity on the glass, and this 
had the effect of breaking the filaments. When this 
method of dusting was discontinued the trouble ceased, and 
the lamps lasted their proper number of hours. 


8 


CHAPTER II 


ELECTRICAL MACHINES AND THE LEYDEN JAR 

The amount of electricity produced by the rubbing of glass 
or sealing-wax rods is very small, and experimenters soon 
felt the need of apparatus to produce larger quantities. In 
1675 the first electrical machine was made by Otto von 
Guericke, the inventor of the air-pump. His machine con¬ 
sisted of a globe of sulphur fixed on a spindle, and rotated 
while the hands were pressed against it to provide the 
necessary friction. Globes and cylinders of glass soon 
replaced the sulphur globe, and the friction was produced 
by cushions instead of by the hands. Still later, revolving 
plates of glass were employed. These machines worked 
well enough in a dry atmosphere, but were very trouble¬ 
some in wet weather, and they are now almost entirely 
superseded by what are known as influence machines. 

In order to understand the working of influence 
machines, it is necessary to have a clear idea of what is 
meant by the word influence as used in an electrical sense. 
In the previous chapter we saw that a pith ball was 
attracted by an electrified body, and that when the ball 
touched that body it received a charge of electricity. 
We now have to learn that one body can receive a charge 
from another body without actual contact, by what is called 
“influence,” or electro-static induction. In Fig. 2 is seen a 
simple arrangement for showing this influence or induction. 
A is a glass ball, and BC a piece of metal, either solid or 

9 


Electricity 

hollow, made somewhat in the shape of a sausage, and 
insulated by means of its glass support. Three pairs of 
pith balls are suspended from BC as shown. If A is 
electrified positively, and brought near BC, the pith balls 
at B and C repel one another, showing that the ends of 
BC are electrified. No repulsion takes place between the 
two pith balls at the middle, indicating that this part of 
BC is not electrified. If the charges at B and C are tested 
they are found to be of opposite kinds, that at B being 
negative, and that at C positive. Thus it appears that 
the positive charge on A has attracted a negative charge 



Fig. 2. —Diagram to illustrate Electro-static Induction. 


to B, and repelled a positive one to C. If A is taken 
away, the two opposite charges on BC unite and neutralise 
one another, and BC is left in its original uncharged con¬ 
dition, while A is found to have lost none of its own charge. 
If BC is made in two parts, and if these are separated while 
under the influence of A, the two charges cannot unite 
when A is removed, but remain each on its own half of 
BC. In this experiment A is said to have induced electri¬ 
fication on BC. Induction will take place across a con¬ 
siderable distance, and it is not stopped by the interposition 
of obstacles such as a sheet of glass. 

io 














Electrical Machines and the Leyden Jar 

We can now understand why an electrified body 
attracts an unelectrified body, as in our pith ball experi¬ 
ments. If we bring a positively charged glass rod near 
a pith ball, the latter becomes electrified by induction, the 
side nearer the rod receiving a negative, and the farther 
side a positive charge. One half of the ball is therefore 
attracted and the other half repelled, but as the attracted 
half is the nearer, the attraction is stronger than the re¬ 
pulsion, and so the ball moves towards the rod. 

Fig. 3 shows an appliance for obtaining strong charges 
of electricity by influence or induction. It is called the 
electrophorus , the name coming from two Greek words, 
electron , amber, and phero, 

I yield or bear; and it was 
devised in 1775 by Volta, an 
Italian professor of physics. 

The apparatus consists of a 
round cake, A, of some 
resinous material contained 
in a metal dish, and a round 
disc of metal, B, of slightly 
smaller diameter, fitted with 
an insulating handle. A simple electrophorus may be 
made by filling with melted sealing-wax the lid of a 
round tin, the disc being made of a circular piece of 
copper or brass, a little smaller than the lid, fastened to 
the end of a stick of sealing-wax. To use the electro¬ 
phorus, the sealing-wax is electrified negatively by rubbing 
it with flannel. The metal disc is then placed on the 
sealing-wax, touched for an instant with the finger, and 
lifted away. The disc is now found to be electrified 
positively, and it may be discharged and the process re¬ 
peated many times without recharging the sealing-wax. 
The charge on the latter is not used up in the process, 

11 














Electricity 

but it gradually leaks away, and after a time it has to 
be renewed. 

The theory of the electrophorus is easy to understand 
from what we have already learnt about influence. When 
the disc B is placed on the charged cake A, the two sur¬ 
faces are really in contact at only three or four points, 
because neither of them is a true plane ; so that on the 
whole the disc and the cake are like A and BC in Fig. 2, 
only much closer together. The negative charge on 

A acts by induction 
on the disc B, attract¬ 
ing a positive charge 
to the under side, and 
repelling a negative 
charge to the upper 
side. When the disc 
is touched, the nega¬ 
tive charge on the 
upper side escapes, but 
the positive charge 
remains, being as it 
were held fast by the 

attraction of the nega- 
FlG. 4. —Wimshurst Machine. . . A Tr 

tive charge on A. 11 

the disc is now raised, the positive charge is no longer 

bound on the under side, and it therefore spreads over 

both surfaces, remaining there because its escape is cut 

off by the insulating handle. 

We may now try to understand the working of influence 
machines, which are really mechanically worked electro- 
phori. There are various types of such machines, but the 
one in most general use in this country is that known as 
the Wimshurst machine, Fig. 4, and we will therefore 
confine ourselves to this. It consists of two circular plates 

12 





















































Electrical Machines and the Leyden Jar 

of varnished glass or of ebonite, placed close together and 
so geared that they rotate in opposite directions. On the 
outer surfaces of the plates are cemented sectors of metal 
foil, at equal distances apart. Each plate has the same 
number of sectors, so that at any given moment the sectors 
on one plate are exactly opposite those on the other. 
Across the outer surface of each plate is fixed a rod of 
metal carrying at its ends light tinsel brushes, which are 
adjusted to touch the sectors as they pass when the plates 
are rotated. These rods are placed at an angle to each 
other of from sixty to ninety degrees, and the brushes are 
called neutralizing brushes. The machine is now complete 
for generating purposes, but in order to collect the electricity 
two pairs of insulated metal combs are provided, one pair 
at each end of the horizontal diameter, with the teeth 
pointing inward towards the plates, but not touching them. 
The collecting combs are fitted with adjustable discharging 
rods terminating in round knobs. 

The principle upon which the machine works will be 
best understood by reference to Fig. 5. In this diagram 
the inner circle represents the front plate, with neutralizing 
brushes A and B, and the outer one represents the back 
plate, with brushes C and D. The sectors are shown 
heavily shaded. E and F are the pairs of combs, and the 
plates rotate in the direction of the arrows. Let us suppose 
one of the sectors at the top of the back plate to have a 
slight positive charge. As the plates rotate this sector will 
come opposite to a front plate sector touched by brush A, 
and it will induce a slight negative charge on the latter 
sector, at the same time repelling a positive charge along 
the rod to the sector touched by brush B. The two sectors 
carrying the induced charges now move on until opposite 
back plate sectors touched by brushes C and D, and these 
back sectors will receive by induction positive and negative 

13 


Electricity 

charges respectively. This process continues as the plates 
rotate, and finally all the sectors moving towards comb E 
will be positively charged, while those approaching comb 
F will be negatively charged. The combs collect these 
charges, and the discharging rods K and L become highly 



Fig. 5. —Diagram to illustrate working of a Wimshurst Machine. 


electrified, K positively and L negatively, and if they are 
near enough together sparks will pass between them. 

At the commencement we supposed one of the sectors 
to have a positive charge, but it is not necessary to charge 
a sector specially, for the machine is self-starting. Why 
this is the case is not yet thoroughly understood, but prob¬ 
ably the explanation is that at any particular moment no 
two places in the atmosphere are in exactly the same 

H 

























Electrical Machines and the Leyden Jar 

electro-static condition, so that an uneven state of charge 
exists permanently amongst the sectors. 

The Wimshurst machine provides us with a plentiful 
supply of electricity, and the question naturally arises, 
“ Can this electricity be stored up in any way ? ” In 1745, 
long before the days of influence machines, a certain Bishop 
of Pomerania, Von Kleist by name, got the idea that if he 
could persuade a charge of electricity to go into a glass 
bottle he would be able to capture it, because glass was a 
non-conductor. So he partly filled a bottle with water, led 
a wire down into the water, and while holding the bottle in 
one hand connected the wire to a primitive form of electric 
machine. When he thought he had got enough electricity 
he tried to remove his bottle in order to examine the con¬ 
tents, and in so doing he received a shock which scared 
him considerably. He had succeeded in storing electricity 
in his bottle. Shortly afterwards the bishop’s experiment 
was repeated by Professor Muschenbrock of Leyden, and 
by his pupil Cuneus, the former being so startled by the 
shock that he wrote, “ I would not take a second shock for 
the kingdom of France.” But in spite of shocks the end 
was achieved ; it was proved that electricity could be col¬ 
lected and stored up, and the bottle became known as the 
Leyden jar. The original idea was soon improved upon, 
water being replaced by a coating of tinfoil, and it was 
found that better results were obtained by coating the 
outside of the bottle as well as the inside. 

As now used the Leyden jar consists of a glass jar 
covered inside and outside with tinfoil up to about two-thirds 
of its height. A wooden lid is fitted, through which passes 
a brass rod terminating above in a brass knob, and below 
in a piece of brass chain long enough to touch the foil 
lining. A Leyden jar is charged by holding it in one 
hand with its knob presented to the discharging ball of a 

i5 


Electricity 

Wimshurst machine, and even if the machine is small and 
feeble the jar will accumulate electricity until it is very 
highly charged. It may now be put down on the table, 
and if it is clean and quite dry it will hold its charge for 
some time. If the outer and inner coatings of the jar are 
connected by means of a piece of metal, the electricity will 
be discharged in the form of a bright spark. A Leyden 
jar is usually discharged by means of discharging tongs, 
consisting of a jointed brass rod with brass terminal 
knobs and glass handles. One knob is placed in contact 
with the outer coating of foil, and the other brought near 
to the knob of the jar, which of course is connected with 
the inner coating. 

The electrical capacity of even a small Leyden jar is 
surprisingly great, and this is due to the mutual attraction 
between opposite kinds of electricity. If we stick a piece 
of tinfoil on the centre of each face of a pane of glass, and 
charge one positively .and the other negatively, the two 
charges attract each other through the glass ; and in fact 
they hold on to each other so strongly that we can get very 
little electricity by touching either piece of foil. This 
mutual attraction enables us to charge the two pieces of 
foil much more strongly than if they were each on a 
separate pane, and this is the secret of the working of the 
Leyden jar. If the knob of the jar is held to the positive 
ball of a Wimshurst, the inside coating receives a positive 
charge, which acts inductively on the outside coating, 
attracting a negative charge to the inner face of the latter, 
and repelling a positive charge to its outer face, and thence 
away through the hand. The electricity is entirely con¬ 
fined to the sides of the jar, the interior having no charge 
whatever. 

Leyden jars are very often fitted to a Wimshurst 
machine as shown at a , a , Fig. 4, and arranged so that they 

16 


Electrical Machines and the Leyden Jar 

can be connected or disconnected to the collecting- combs 
as desired. When the jars are disconnected the machine 
gives a rapid succession of thin sparks, but when the jars 
are connected to the combs they accumulate a number of 
charges before the discharge takes place, with the result 
that the sparks are thicker, but occur at less frequent 
intervals. 

It will have been noticed that the rod of a Leyden jar 
and the discharging rods of a Wimshurst machine are 
made to terminate not in points, but in rounded knobs or 
balls. The reason of this is that electricity rapidly leaks 
away from points. If we electrify a conductor shaped like 
a cone with a sharp point, the density of the electricity is 
greatest at that point, and when it becomes sufficiently 
great the particles of air near the point become electrified 
and repelled. Other particles take their place, and are 
electrified and repelled in the same way, and so a constant 
loss of electricity takes place. This may be shown in an 
interesting way by fastening with wax a needle to the knob 
of a Wimshurst. If a lighted taper is held to the point of 
the needle while the machine is in action, the flame is 
blown aside by the streams of repelled air, which form a 
sort of electric wind. 


B 


17 


CHAPTER III 


ELECTRICITY IN THE ATMOSPHERE 

If the Leyden jars of a Wimshurst machine are connected 
up and the discharging balls placed at a suitable distance 
apart, the electricity produced by rotating the plates is 
discharged in the form of a brilliant zigzag spark between 
the balls, accompanied by a sharp crack. The resemblance 
between this spark and forked lightning is at once evident, 
and in fact it is lightning in miniature. The discharging 
balls are charged, as we have seen, with opposite kinds of 
electricity, and these charges are constantly trying to reach 
one another across the intervening air, which, being an 
insulator, vigorously opposes their passage. There is thus 
a kind of struggle going on between the air and the two 
charges of electricity, and this keeps the air in a state of 
constant strain. But the resisting power of the air is 
limited, and when the charges reach a certain strength the 
electricity violently forces its way across, literally rupturing 
or splitting the air. The particles of air along the path of 
the discharge are rendered incandescent by the heat pro¬ 
duced by the passage of the electricity, and so the brilliant 
flash is produced. Just as a river winds about seeking the 
easiest course, so the electricity takes the path of least 
resistance, which probably is determined by the particles 
of dust in the air, and also by the density of the air, which 
becomes compressed in front, leaving less dense air and 
therefore an easier path on each side. 

18 


Electricity in the Atmosphere 

The connexion between lightning and the sparks from 
electrified bodies and electrical machines was suspected by 
many early observers, but it remained for Benjamin 
Franklin to prove that lightning was simply a tremendous 
electric discharge, by actually obtaining electricity from a 
thunder-cloud. Franklin was an American, born at Boston 
in 1706. He was a remarkable man in every way, and 
quite apart from his investigations in electricity, will always 
be remembered for the great public services he rendered to 
his country in general and to Philadelphia in particular. 
He founded the Philadelphia Library, the American Philo¬ 
sophical Society, and the University of Pennsylvania. 

Franklin noticed many similarities between electricity 
and lightning. For instance, both produced zigzag sparks, 
both were conducted by metals, both set fire to inflammable 
materials, and both were capable of killing animals. These 
resemblances appeared to him so striking that he was 
convinced that the two were the same, and he resolved to 
put the matter to the test. For this purpose he hit upon 
the idea of using a kite, to the top of which was fixed a 
pointed wire. At the lower end of the flying string was 
tied a key, insulated by a piece of silk ribbon. In June 
1752, Franklin flew his kite, and after waiting a while he 
was rewarded by finding that when he brought his knuckle 
near to the key a little spark made its appearance. This 
spark was exactly like the sparks obtained from electrified 
bodies, but to make things quite certain a Leyden jar was 
charged from the key. Various experiments were then 
performed with the jar, and it was proved beyond all doubt 
that lightning and electricity were one and the same. 

Lightning is then an enormous electric spark between a 
cloud and the Earth, or between two clouds, produced when 
opposite charges become so strong that they are able to 
break down the intervening non-conducting layer of air. 

19 


Electricity 

The surface of the Earth is negatively electrified, the 
electrification varying at different times and places; while 
the electricity of the air is usually positive, but frequently 
changes to negative in rainy weather and on other occasions. 
As the clouds float about they collect the electricity from 
the air, and thus they may be either positively or negatively 
electrified, so that a discharge may take place between one 
cloud and another, as well as between a cloud and the Earth. 

Lightning flashes take different forms, the commonest 
being forked or zigzag lightning, and sheet lightning. 
The zigzag form is due to the discharge taking the easiest 
path, as in the case of the spark from a Wimshurst machine. 
Sheet lightning is probably the reflection of a flash taking 
place at a distance. It may be unaccompanied by thunder, 
as in the so-called “ summer lightning,” seen on the horizon 
at night, which is the reflection of a storm too far off for the 
t-liimeter to be heard. A much rarer form is globular or 
baH lightning, in which the discharge takes the shape of a 
ball of light, which moves slowly along and finally dis¬ 
appears with a sudden explosion. The cause of this form 
of lightning is not yet understood, but it is possible that the 
ball of light consists of intensely heated and extremely 
minute fragments of ordinary matter, torn off by the 
violence of the lightning discharge. Another uncommon 
form is multiple lightning, which consists of a number of 
separate parallel discharges having the appearance of a 
ribbon. 

A lightning flash probably lasts from about rvv.Tnnr to 
T.oov.uTro of a second, and in the majority of cases the 
discharge is oscillatory ; that is to say, it passes several times 
backwards and forwards between two clouds or between a 
cloud and the Earth. At times it appears as though we 
could see the lightning start downwards from the cloud or 
upwards from the Earth, but this is an optical illusion, and 

20 





Electricity in the Atmosphere 

it is really quite impossible to tell at which end the flash 
starts. 

Death by lightning is instantaneous, and therefore 
quite painless. We are apt to think that pain is felt at the 
moment when a wound is inflicted. This is not the case 
however, for no pain is felt until the impression reaches the 
brain by way of the nerves, and this takes an appreciable 
time. The nerves transmit sensations at a speed of only 
about one hundred feet per second, so that in the case of a 
man killed by a bullet through the brain, no pain would be 
felt, because the brain would be deprived of sensibility 
before the sensation could reach it. Lightning is infinitely 
swifter than any bullet, so life would be destroyed by it 
before any pain could be felt. 

On one occasion Professor Tyndall, the famous 
physicist, received accidentally a very severe shock from 
a large battery of Leyden jars while giving a public lecture. 
His account of his sensations is very interesting. “ Life 
was absolutely blotted out for a very sensible interval, 
without a trace of pain. In a second or so consciousness 
returned ; I saw myself in the presence of the audience and 
apparatus, and, by the help of these external appearances, 
immediately concluded that I had received the battery dis¬ 
charge. The intellectual consciousness of my position was 
restored with exceeding rapidity, but not so the optical 
consciousness. To prevent the audience from being 
alarmed, I observed that it had often been my desire to 
receive accidentally such a shock, and that my wish had at 
length been fulfilled. But, while making this remark, the 
appearance which my body presented to myself was that of 
a number of separate pieces. The arms, for example, were 
detached from the trunk, and seemed suspended in the air. 
In fact, memory and the power of reasoning appeared to 
be complete long before the optic nerve was restored to 


Electricity 

healthy action. But what I wish chiefly to dwell upon 
here is, the absolute painlessness of the shock ; and there 
cannot be a doubt that, to a person struck dead by lightning, 
the passage from life to death occurs without consciousness 
being in the least degree implicated. It is an abrupt 
stoppage of sensation, unaccompanied by a pang.” 

Occasionally branched markings are found on the 
bodies of those struck by lightning,f and these are often 
taken to be photographic impressions of trees under which 
the persons may have been standing at the time of the 
flash. The markings however are nothing of the kind, 
but are merely physiological effects due to the passage of 
the discharge. 

During a thunderstorm it is safer to be in the house 
than out in the open. It is probable that draughts are a 
source of some danger, and the windows and doors of the 
room ought to be shut. Animals are more liable to be 
struck by lightning than men, and a shed containing 
horses or cows is a dangerous place in which to take 
shelter; in fact it is better to remain in the open. If one 
is caught in a storm while out of reach of a house or other 
building free from draughts and containing no animals, 
the safest plan is to lie down, not minding the rain. 
Umbrellas are distinctly dangerous, and never should be 
used during a storm. Wire fences, hedges, and still or 
running water should be given a wide berth, and it is 
safer to be alone than in company with a crowd of people. 
It is extremely foolish to take shelter under an isolated 
tree, for such trees are very liable to be struck. Isolated 
beech trees appear to have considerable immunity from 
lightning, but any tree standing alone should be avoided, 
the oak being particularly dangerous. On the other hand, 
a fairly thick wood is comparatively safe, and failing a 
house, should be chosen before all other places of refuge. 

22 


Electricity in the Atmosphere 

Horses are liable to be struck, and if a storm comes on 
while one is out driving it is safer to keep quite clear of the 
animals. 

When a Wimshurst machine has been in action for a 
little time a peculiar odour is noticed. This is due to the 
formation of a modified and chemically more active form of 
oxygen, called ozone , the name being derived from the 
Greek ozein , “ to smell.” Ozone has very invigorating effects 
when breathed, and it is also a powerful germicide, capable 
of killing the germs which give rise to contagious diseases. 
During a thunderstorm ozone is produced in large 
quantities by the electric discharges, and thus the air 
receives as it were a new lease of life, and we feel the 
refreshing effects when the storm is over. We shall speak 
again of ozone in Chapter XXV. 

Thunder probably is caused by the heating and sudden 
expansion of the air in the path of the discharge, which 
creates a partial vacuum into which the surrounding air 
rushes violently. Light travels at the rate of 186,000 
miles per second, and therefore the flash reaches us 
practically instantaneously ; but sound travels at the rate of 
only about 1115 feet per second, so that the thunder takes 
an appreciable time to reach us, and the farther away the 
discharge the greater the interval between the flash and 
the thunder. Thus by multiplying the number of seconds 
which elapse between the flash and the thunder by 1115, 
we may calculate roughly the distance in feet of the 
discharge. A lightning flash may be several miles in 
length, the greatest recorded length being about ten miles. 
The sounds produced at different points along its path 
reach us at different times, producing the familiar sharp 
rattle, and the following rolling and rumbling is produced 
by the echoes from other clouds. The noise of a thunder¬ 
clap is so tremendous that it seems as though the sound 

23 


Electricity 

would be heard far and wide, but the greatest distance at 
which thunder has been heard is about fifteen miles. In 
this respect it is interesting to compare the loudest 
thunder-clap we ever heard with the noise of the famous 
eruption of Krakatoa, in 1883, which was heard at the 
enormous distance of nearly three thousand miles. 

When Franklin had demonstrated the nature of 
lightning, he began to consider the possibility of protecting 
buildings from the disastrous effects of the lightning stroke. 
At that time the amount of damage caused by lightning 
was very great. Cathedrals, churches, public buildings, 
and in fact all tall edifices were in danger every time a 
severe thunderstorm took place in their neighbourhood, for 
there was absolutely nothing to prevent their destruction if 
the lightning chanced to strike them. Ships at sea, too, 
were damaged very frequently by lightning, and often 
some of the crew were killed or disabled. To-day, thanks 
to the lightning conductor, it is an unusual occurrence for 
ships or large buildings to be damaged by lightning. The 
lightning strikes them as before, but in the great majority 
of cases it is led away harmlessly to earth. 

Franklin was the first to suggest the possibility of 
protecting buildings by means of a rod of some conducting 
material terminating in a point at the highest part of the 
building, and leading down, outside the building, into the 
earth. Lightning conductors at the present day are 
similar to Franklin’s rod, but many improvements have 
been made from time to time as our knowledge of the 
nature and action of the lightning discharge has increased. 
A modern lightning conductor generally consists of one or 
more pointed rods fixed to the highest parts of the building, 
and connected to a cable running directly to earth. This 
cable is kept as straight as possible, because turns and 
bends offer a very high resistance to the rapidly oscillating 

24 


Electricity in the Atmosphere 

discharge; and it is connected to large copper plates 
buried in permanently moist ground or in water, or to 
water or gas mains. Copper is generally used for the 
cable, but iron also may be employed. In any case, the 
cable must be of sufficient thickness to prevent the 
possibility of its being deflagrated by the discharge. In 
ships the arrangements are similar, except that the cable is 
connected to the copper sheathing of the bottom. 

d he fixing of lightning conductors must be carried out 
with great care, for an improperly fixed conductor is not 
only useless, but may be a source of actual danger. 
Lightning flashes vary greatly in character, and while a 
carefully erected lightning conductor is capable of dealing 
with most of them, there are unfortunately certain kinds of 
discharge with which it now and then is unable to deal. 
The only absolutely certain way of protecting a building is 
to surround it completely by a sort of cage of metal, but 
except for buildings in which explosives are stored this 
plan is usually impracticable. 

The electricity of the atmosphere manifests itself in 
other forms beside the lightning. The most remarkable 
of these manifestations is the beautiful phenomenon known 
in the Northern Hemisphere as the Aurora Borealis, and 
in the Southern Hemisphere as the Aurora Australis. 
Aurora means the morning hour or dawn, and the pheno¬ 
menon is so called from its resemblance to the dawn of 
day. The aurora is seen in its full glory only in high 
latitudes, and it is quite unknown at the equator. It 
assumes various forms, sometimes appearing as an arch of 
light with rapidly moving streamers of different colours, 
and sometimes taking the form of a luminous curtain 
extending across the sky. The light of the aurora is never 
very strong, and as a rule stars can be seen through it. 
Auroras are sometimes accompanied by rustling or crack- 

25 


Electricity 

ling sounds, but the sounds are always extremely faint. 
Some authorities assert that these sounds do not exist, and 
that they are the result of imagination, but other equally 
reliable observers have heard the sounds quite plainly on 
several occasions. Probably the explanation of this con- 
fliction of evidence is that the great majority of auroras are 
silent, so that an observer might witness many of them 
without hearing any sounds. The height at which auroras 
occur is a disputed point, and one which it is difficult to 
determine accurately; but most observers agree that it 
is generally from 60 to 125 miles above the Earth’s 
surface. 

There is little doubt that the aurora is caused by the 
passage of electric discharges through the higher regions 
of the atmosphere, where the air is so rarefied as to act as 
a partial conductor; and its effects can be imitated in some 
degree by passing powerful discharges through tubes from 
which the air has been exhausted to a partial vacuum. 
Auroral displays are usually accompanied by magnetic 
disturbances, which sometimes completely upset telegraphic 
communication. Auroras and magnetic storms appear to 
be connected in some way with solar disturbances, for they 
are frequently simultaneous with an unusual number of 
sunspots, and all three run in cycles of about eleven and a 
half years. 


* 


2 6 


I 


CHAPTER IV 

THE ELECTRIC CURRENT 

In the previous chapters we have dealt with electricity in 
charged bodies, or static electricity, and now we must turn 
to electricity in motion, or current electricity. In Chapter I. 
we saw that if a metal rod is held in the hand and rubbed, 
electricity is produced, but it immediately escapes along the 
rod to the hand, and so to the earth. In other words, the 
electricity flows away along the conducting path provided 
by the rod and the hand. When we see the word “ flow ” we 
at once think of a fluid of some kind, and we often hear 
people speak of the “electric fluid.” Now, whatever 
electricity may be it certainly is not a fluid, and we use 
the word “ flow ” in connexion with electricity simply because 
it is the most convenient word we can find for the purpose. 
Just in the same way we might say that when we hold a 
poker with its point in the fire, heat flows along it towards 
our hand, although we know quite well that heat is not a 
fluid. In the experiment with the metal rod referred to 
above, the electricity flows away instantly, leaving the rod 
unelectrified; but if we arrange matters so that the 
electricity is renewed as fast as it flows away, then we get 
a continuous flow, or current. 

Somewhere about the year i78oan Italian anatomist, 
Luigi Galvani, was studying the effects of electricity upon 
animal organisms, using for the purpose the legs of freshly 
killed frogs. In the course of his experiments he happened 
to hang against an iron window rail a bundle of frogs’ legs 

27 


Electricity 

fastened together with a piece of copper wire, and he 
noticed that the legs began to twitch in a peculiar manner. 
He knew that a frog’s leg would twitch when electricity 
was applied to it, and he concluded that the twitchings in 
this case were caused in the same way. So far he was 
quite right, but then came the problem of how any 
electricity could be produced in these circumstances, and 

here he went astray. It 
never occurred to him that 
the source of the electricity 
might be found in something 
quite apart from the legs, 
and so he came to the con¬ 
clusion that the phenomenon 
was due to electricity pro¬ 
duced in some mysterious 
way in the tissues of the 
animal itself. He therefore 
announced that he had dis¬ 
covered the existence of a 
kind of animal electricity, 
and it was left for his fellow- 
countryman, Alessandro 
Volta, to prove that the 
twitchings were due to elec¬ 
tricity produced by the con¬ 
tact of the two metals, the iron of the window rail and the 
copper wire. 

Volta found that when two different metals were placed in 
contact in air, one became positively charged, and the other 
negatively. These charges however were extremely feeble, 
and in his endeavours to obtain stronger results he hit upon 
the idea of using a number of pairs of metals, and he con¬ 
structed the apparatus known as the Voltaic pile, Fig. 6. 

28 















































The Electric Current 

This consists of a number of pairs of zinc and copper 
discs, each pair being - separated from the next pair by a 
disc of cloth moistened with salt water. These are piled 
up and placed in a frame, as shown in the figure. One 
end of the pile thus terminates in a zinc disc, and the other 
in a copper disc, and as soon as the two are connected by 
a wire or other conductor a continuous current of electricity 
is produced. The cause of the electricity produced by the 
voltaic pile was the subject of 
a long and heated controversy. 

There were two main theories ; 
that of Volta himself, which 
attributed the electricity to the 
mere cont ct of unlike metals, 
and the chemical theory, which 
ascribed it to chemical action. 

The chemical theory is now 
generally accepted, but certain 
points, into which we need not 
enter, are still in dispute. 

There is a curious experi¬ 
ment which some of my readers 
may like to try. Place a copper 
coin on a sheet of zinc, and set an 
ordinary garden snail to crawl 

across the zinc towards the coin. As soon as the snail 
comes in contact with the copper it shrinks back, and shows 
every sign of having received a shock. One can well 
imagine that an enthusiastic gardener pestered with snails 
would watch this experiment with great glee. 

Volta soon found that it was not necessary to have his 
pairs of metals in actual metallic contact, and that better 
results were got by placing them in a vessel filled with 
dilute acid. Fig. 7 is a diagram of a simple voltaic cell of 

29 



Fig. 7. —Simple Voltaic Cell. 



















Electricity 

this kind, and it shows the direction of the current when 
the zinc and the copper are connected by the wire. In 
order to get some idea of the reason why a current flows 
we must understand the meaning of electric potential. If 
water is poured into a vessel, a certain water pressure is 
produced. The amount of this pressure depends upon the 
level of the water, and this in turn depends upon the 
quantity of water and the capacity of the vessel, for a 
given quantity of water will reach a higher level in a small 
vessel than in a larger one. In the same way, if elec¬ 
tricity is imparted to a conductor an electric pressure is 
produced, its amount depending upon the quantity of 
electricity and the electric capacity of the conductor, for 
conductors vary in capacity just as water vessels do. 

This electric pressure is called “potential,” and electricity 
tends to flow from a conductor of higher to one of lower 
potential. When we say that a place is so many feet 
above or below sea-level we are using the level of the sea 
as a zero level, and in estimating electric potential we take 
the potential of the earth’s surface as zero ; and we regard 
a positively electrified body as one at a positive or re¬ 
latively high potential, and a negatively electrified body as 
one at a negative or relatively low potential. This may be 
clearer if we think of temperature and the thermometer. 
Temperatures above zero are positive and represented by 
the sign +, and those below zero are negative and repre¬ 
sented by the sign —. Thus we assume that an electric 
current flows from a positive to a negative conductor. 

In a voltaic cell the plates are at different potentials, so 
that when they are connected by a wire a current flows, 
and we say that the current leaves the cell at the positive 
terminal, and enters it again at the negative terminal. As 
shown in Fig. 7, the current moves in opposite directions 
inside and outside the cell, making a complete round called 

30 


PLATE I 






















































































































- 







The Electric Current 

a circuit , and if the circuit is broken anywhere the current 
ceases to flow. If the circuit is complete the current keeps 
on flowing, trying to equalize the electric pressure or 
potential, but it is unable to do this because the chemical 
action between the acid and the zinc maintains the differ¬ 
ence of potential between the plates. This chemical action 
results in wasting of the zinc and weakening of the acid, 
and as long as it continues the current keeps on flowing. 
When we wish to stop the current we break the circuit by 
disconnecting the wire joining the terminals, and the cell 
then should be at rest; but owing to the impurities in 
ordinary commercial zinc chemical action still continues. 
In order to prevent wasting when the current is not re¬ 
quired the surface of the zinc is coated with a thin film of 
mercury. The zinc is then said to be amalgamated, and 
it is not acted upon by the acid so long as the circuit 
remains broken. 

The current from a simple voltaic cell does not remain 
at a constant strength, but after a short time it begins to 
weaken rapidly. The cell is then said to be polarized, and 
this polarization is caused by bubbles of hydrogen gas 
which accumulate on the surface of the copper plate during 
the chemical action. These bubbles of gas weaken the 
current partly by resisting its flow, for they are bad con¬ 
ductors, and still more by trying to set up another current 
in the opposite direction. For this reason the simple 
voltaic cell is unsuitable for long spells of work, and many 
cells have been devised to avoid the polarization trouble. 
One of the most successful of these is the Daniell cell. It 
consists of an outer vessel of copper, which serves as the 
copper plate, and an inner porous pot containing a zinc 
rod. Dilute sulphuric acid is put into the porous pot and 
a strong solution of copper sulphate into the outer jar. 
When the circuit is closed, the hydrogen liberated by the 

3i 


Electricity 

action of the zinc on the acid passes through the porous 
pot, and splits up the copper sulphate into copper and 
sulphuric acid. In this way pure copper, instead of 
hydrogen, is deposited on the copper plate, no polarization 
takes place, and the current is constant. 

Other cells have different combinations of metals, such 
as silver-zinc, or platinum-zinc, and carbon is also largely 
used in place of one metal, as in the familiar carbon-zinc 
Leclanch^ cell, used for ringing electric bells. This cell 
consists of an inner porous pot containing a carbon plate 
packed round with a mixture of crushed carbon and man¬ 
ganese dioxide, and an outer glass jar containing a zinc 
rod and a solution of sal-ammoniac. Polarization is 
checked by the oxygen in the manganese dioxide, which 
seizes the hydrogen on its way to the carbon plate, and 
combines with it. If the cell is used continuously however 
this action cannot keep pace with the rate at which the 
hydrogen is produced, and so the cell becomes polarized ; 
but it soon recovers after a short rest. 

The so-called “ dry ” cells so much used at the present 
time are not really dry at all ; if they were they would give 
no current. They are in fact Leclanchd cells, in which 
the containing vessel is made of zinc to take the place of a 
zinc rod ; and they are dry only in the sense that the liquid 
is taken up by an absorbent material, so as to form a moist 
paste. Dry cells are placed inside closely fitting cardboard 
tubes, and are sealed up at the top. Their chief advantage 
lies in their portability, for as there is no free liquid to 
spill they can be carried about and placed in any position. 

We have seen that the continuance of the current from 
a voltaic cell depends upon the keeping up of a difference 
of potential between the plates. The force which serves 
to maintain this difference is called the electro-motive force, 
and it is measured in volts. The actual flow of electricity 

32 


The Electric Current 

is measured in amperes. Probably all my readers are 
familiar with the terms volt and ampere, but perhaps some 
may not be quite clear about the distinction between the 
two. When water flows along a pipe we know that it is 
being forced to do so by pressure resulting from a differ¬ 
ence of level. That is to say, a difference of level pro¬ 
duces a water-moving or water-motive force; and in a 
similar way a difference of potential produces an elec¬ 
tricity-moving or electro-motive force, which is measured 
in volts. If we wish to describe the rate of flow of water 
we state it in gallons per second, and the rate of flow of 
electricity is stated in amperes. Volts thus represent the 
pressure at which a current is supplied, while the current 
itself is measured in amperes. 

We may take this opportunity of speaking of electric 
resistance. A current of water flowing through a pipe is, 
resisted by friction against the inner surface of the pipe ; 
and a current of electricity flowing through a circuit also 
meets with a resistance, though this is not due to friction. 
In a good conductor this resistance is small, but in a bad 
conductor or non-conductor it is very great. The resistance 
also depends upon length and area of cross-section ; so that 
a long wire offers more resistance than a short one, and a 
thin wire more than a thick one. Before any current can 
flow in a circuit the electro-motive force must overcome 
the resistance, and we might say that the volts drive the 
amperes through the resistance. The unit of resistance is 
the ohm, and the definition of a volt is that electro-motive 
force which will cause a current of one ampere to flow 
through a conductor having a resistance of one ohm. These 
units of measurement are named after three famous scientists, 
Volta, Ampere, and Ohm. 

A number of cells coupled together form a battery, and 
different methods of coupling are used to get different 
c 33 


Electricity 

results. In addition to the resistance of the circuit outside 
the cell, the cell itself offers an internal resistance, and part 
of the electro-motive force is used up in overcoming this 
resistance. If we can decrease this internal resistance we 
shall have a larger current at our disposal, and one way of 
doing this is to increase the size of the plates. This of 
course means making the cell larger, and very large cells 
take up a lot of room and are troublesome to move about. 
We can get the same effect however by coupling. If we 
connect together all the positive terminals and all the 
negative terminals of several cells, that is, copper to copper 



Fig. 8. —Cells connected in Parallel. 


and zinc to zinc in Daniell cells, we get the same result as 
if we had one very large cell. The current is much larger, 
but the electro-motive force remains the same as if only 
one cell were used, or in other words we have more amperes 
but no more volts. This is called connecting in “ parallel,” 
and the method is shown in Fig. 8. On the other hand, 
if, as is usually the case, we want a larger electro-motive 
force, we connect the positive terminal of one cell to the 
negative terminal of the next, or copper to zinc all through. 
In this way we add together the electro-motive forces of all 
the cells, but the amount of current remains that of a single 
cell; that is, we get more volts but no more amperes. This is 
called connecting in “ series,” and the arrangement is shown 

34 

























The Electric Current 

in Fig. 9. We can also increase both volts and amperes by 
combining the two methods. 

A voltaic cell gives us a considerable quantity of 
electricity at low pressure, the electro-motive force of a 
Leclanchd cell being about 1J volts, and that of a Daniell 
cell about 1 volt. We may perhaps get some idea of the 
electrical conditions existing during a thunderstorm from 
the fact that to produce a spark one mile long through air 
at ordinary pressure we should require a battery of more 
than a thousand million Daniell cells. Cells such as we 



Fig. 9.—Cells connected in Series. 


have described in this chapter are called primary cells, as 
distinguished from accumulators, which are called secondary 
cells. Some of the practical applications of primary cells 
will be described in later chapters. 

Besides the voltaic cell, in which the current is produced 
by chemical action, there is the thermo-electric battery, or 
thermopile, which produces current directly from heat 
energy. About 1822 Seebeck was experimenting with 
voltaic pairs of metals, and he found that a current could 
be produced in a complete metallic circuit consisting of 
different metals joined together, by keeping these joinings 
at different temperatures. Fig. 10 shows a simple arrange¬ 
ment for demonstrating this effect, which is known as the 

35 






















B 



Fig. io. —Diagram to illustrate the 
Seebeck effect. 


Electricity 

“ Seebeck effect.’’ A slab of bismuth, BB, has placed upon it 
a bent strip of copper, C. If one of the junctions of the 
two metals is heated as shown, a current flows ; and the 

same effect is produced 
by cooling one of the 
junctions. This cur¬ 
rent continues to flow 
as long as the two junc¬ 
tions are kept at differ¬ 
ent temperatures. In 
1834 another scientist, 
Peltier, discovered that 
if a current was passed 
across a junction of two different metals, this junction was 
either heated or cooled, according to the direction in which 
the current flowed. In Fig. 10 the current across the 
heated junction tends to cool the junction, while the Bunsen 
burner opposes this cooling, and keeps up the temperature. 
A certain amount of the heat energy is thus transformed 
into electrical 
energy. At the 
other junction 
the current 
produces a 
heating effect, 
so that some of 
the electrical 
energy is re¬ 
transformed 
into heat. 

A thermopile consists of a number of alternate bars or 
strips of two unlike metals, joined together as shown 
diagrammatically in Fig. 11. The arrangement is such 
that the odd junctions are at one side, and the even ones 

3b 



Fig. 11.—Diagram to show arrangement of two 
different metals in Thermopile. 





The Electric Current 

at the other. The odd junctions are heated, and the even 
ones cooled, and a current flows when the circuit is com¬ 
pleted. By using a larger number of junctions, and by 
increasing the difference of temperature between them, the 
voltage of the current may be increased. Thermopiles are 
nothing like so efficient as voltaic cells, and they are more 
costly. They are used to a limited extent for purposes 
requiring a very small and constant current, but for 
generating considerable quantities of current at high 
pressure they are quite useless. The only really important 
practical use of the thermopile is in the detection and 
measurement of very minute differences of temperature, 
which are beyond the capabilities of the ordinary thermo¬ 
meter. Within certain limits, the electro-motive force of a 
thermopile is exactly proportionate to the difference of 
temperature. The very slightest difference of temperature 
produces a current, and by connecting the wires from a 
specially constructed thermopile to a delicate instrument 
for measuring the strength of the current, temperature 
differences of less than one-millionth of a degree can be 
detected. 


37 


CHAPTER V 


THE ACCUMULATOR 

If we had two large water tanks, one of which could be 
emptied only by allowing the bottom to fall completely out, 
and the other by means of a narrow pipe, it is easy to see 
which would be the more useful to us as a source of water 
supply. If both tanks were filled, then from the first we 
could get only a sudden uncontrollable rush of water, but 
from the other we could get a steady stream extending over 
a long period, and easily controlled. The Leyden jar stores 
electricity, but in yielding up its store it acts like the first 
tank, giving a sudden discharge in the form of a bright 
spark. We cannot control the discharge, and therefore we 
cannot make it do useful work for us. For practical 
purposes we require a storing arrangement that will act like 
the second tank, giving us a steady current of electricity 
for a long period, and this we have in the accumulator or 
storage cell. 

A current of electricity has the power of decomposing 
certain liquids. If we pass a current through water, the 
water is split up into its two constituent gases, hydrogen 
and oxygen, and this may be shown by the apparatus seen 
in Fig. 12. It consists of a glass vessel with two strips of 
platinum to which the current is led. The vessel contains 
water to which has been added a little sulphuric acid to 
increase its conducting power, and over the strips are in¬ 
verted two test-tubes filled with the acidulated water. The 

38 


The Accumulator 

platinum strips, which are called electrodes , are connected 
to a battery of Daniell cells. When the current passes, 
the water is decomposed, and oxygen collects at the electrode 
connected to the positive terminal of the battery, and 
hydrogen at the other electrode. The two gases rise up 
into the test-tubes and displace the water in them, and the 
whole process is called the electrolysis of water. If now 
we disconnect the battery and join the two electrodes by 
a wire, we find that a current flows from the apparatus 
as from a voltaic cell, but 
in the opposite direction 
from the original battery 
current. 

It will be remembered 
that one of the troubles 
with a simple voltaic cell 
was polarization, caused 
by the accumulation of 
hydrogen; and that this 
weakened the current by 
setting up an opposing 
electro-motive force tend¬ 
ing to produce another 
current in the opposite 
direction. In the present 
case a similar opposing or back electro-motive force is 
produced, and as soon as the battery current is stopped 
and the electrodes are connected, we get a current in the 
reverse direction, and this current continues to flow until 
the two gases have recombined, and the electrodes have 
regained their original condition. Consequently we can 
see that in order to electrolyze water, our battery must 
have an electro-motive force greater than that set up in 
opposition to it, and at least two Daniell cells are required. 

39 





Fig. 12.—Diagram showing Electrolysis 
of Water. 















Electricity 

This apparatus thus may be made to serve to some 
extent as an accumulator or storage cell, and it also serves 
to show that an accumulator does not store up or accumulate 
electricity. In a voltaic cell we have chemical energy 
converted into electrical energy, and here we have first 
electrical energy converted into chemical energy, and then 
the chemical energy converted back again into electrical 
energy. This is a rough-and-ready way of putting the 
matter, but it is good enough for practical purposes, and at 
any rate it makes it quite clear that what an accumulator 
really stores up is not electricity, but energy, which is given 
out in the form of electricity. 

The apparatus just described is of little use as a source 
of current, and the first really practical accumulator was 
made in 1878 by Gaston Plantd. The electrodes were two 
strips of sheet lead placed one upon the other, but separated 
by some insulating material, and made into a roll. This 
roll was placed in dilute sulphuric acid, and one strip or 
plate connected to the positive, and the other to the 
negative terminal of the source of current. The current 
was passed for a certain length of time, and then the accumu¬ 
lator partly discharged ; after which current was passed 
again, but in the reverse direction, followed by another period 
of discharge. This process, which is called forming , 
was continued for several days, and its effect was to change 
one plate into a spongy condition, and to form a coating 
of peroxide of lead on the other. When the plates were 
properly formed the accumulator was ready to be fully 
charged and put into use. The effect of charging was to 
rob one plate of its oxygen, and to transfer this oxygen to 
the other plate, which thus received an overcharge of the 
gas. During the discharge of the accumulator the excess 
of oxygen went back to the place from which it had been 
taken, and the current continued until the surfaces of both 

40 


The Accumulator 

plates were reduced to a chemically inactive state. The 
accumulator could be charged and discharged over and 
over again as long as the plates remained in good order. 

In 1881, Faure hit upon the idea of coating the plates 
with a paste of red-lead, and this greatly shortened the 
time of forming. At first it was found difficult to make the 
paste stick to the plates, but this trouble was got rid of by 
making the plates in the form of grids, and pressing the 
paste into the perforations. Many further improvements 
have been made from time to time, but instead of tracing 
these we will go on at once to the description of a present- 
day accumulator. There are now many excellent accumu¬ 
lators made, but we have not space to consider more than 
one, and we will select that known as the “ Chloride ” 
accumulator. 

The positive plate of this accumulator is of the Plante 
type, but it is not simply a casting of pure lead, but is made 
by a building-up process which allows of the use of a 
lead-antimony mixture for the grids. This gives greater 
strength, and the grids themselves are unaffected by the 
chemical changes which take place during the charging and 
discharging of the cell. The active material, that is the 
material which undergoes chemical change, is pure lead 
tape coiled up into rosettes, which are so designed that the 
acid can circulate through the plates. These rosettes are 
driven into the perforations of the grid by a hydraulic press, 
and during the process of forming they expand and thus 
become very firmly fixed. The negative plate has a frame 
made in two parts, which are riveted together after the 
insertion of the active material, which is thus contained in 
a number of small cages. The plate is covered outside 
with a finely perforated sheet of lead, which prevents the 
active material from falling out. It is of the utmost 
importance that the positive and negative plates should be 

4i 


Electricity 

kept apart when in the cell, and in the Chloride accumula¬ 
tor this is ensured by the use of a patent separator made of 
a thin sheet of wood the size of the plates. Before being 
used the wood undergoes a special treatment to remove all 
substances which might be harmful, and it then remains 
unchanged either in appearance or composition. Other 
insulating substances, such as glass rods or ebonite forks, 
can be used as separators, but it is claimed that the wood 
separator is not only more satisfactory, but that in some 
unexplained way it actually helps to keep up the capacity 
of the cell. The plates are placed in glass, or lead-lined 
wood or metal boxes, and are suspended from above the 
dilute sulphuric acid with which the cells are filled. A 
space is left below the plates for the sediment which 
accumulates during the working of the cell. 

In all but the smallest cells several pairs of plates are 
used, all the positive plates being connected together and 
all the negative plates. This gives the same effect as two 
very large plates, on the principle of connecting in parallel, 
spoken of in Chapter IV. A single cell, of whatever size, 
gives current at about two volts, and to get higher voltages 
many cells are connected in series, as with primary cells. 
The capacity is generally measured in ampere-hours. Foe 
instance, an accumulator that will give a current of eight 
amperes for one hour, or of four amperes for two hours, or 
one ampere for eight hours, is said to have a capacity of 
eight ampere-hours. 

Accumulators are usually charged from a dynamo or 
from the public mains, and the electro-motive force of 
the charging current must be not less than 2\ volts for 
each cell, in order to overcome the back electro-motive 
force of the cells themselves. It is possible to charge 
accumulators from primary cells, but except on a very 
small scale the process is comparatively expensive. Non- 

42 


The Accumulator 

polarizing cells, such as the Daniell, must be used for this 
purpose. 

The practical applications of accumulators are almost 
innumerable, and year by year they increase. As the most 
important of these are connected with the use of electricity 
for power and light, it will be more convenient to speak of 
them in the chapters dealing with this subject. Minor 
uses of accumulators will be referred to briefly from time 
to time in other chapters. 


43 


CHAPTER VI 


MAGNETS AND MAGNETISM 

In many parts of the world there is to be found a kind of 
iron ore, some specimens of which have the peculiar power 
of attracting iron, and of turning to the north if suspended 
freely. This is called the lodestone , and it has been 
known from very remote times. The name Magnetism has 
been given to this strange property of the lodestone, but the 
origin of the name is not definitely known. There is an 
old story about a shepherd named Magnes, who lived in 
Phrygia in Asia Minor. One day, while tending his sheep 
on Mount Ida, he happened to touch a dark coloured rock 
with the iron end of his crook, and he was astonished and 
alarmed to find that the rock was apparently alive, for it 
gripped his crook so firmly that he could not pull it away. 
This rock is said to have been a mass of lodestone, and 
some people believe that the name magnet comes from the 
shepherd Magnes. Others think that the name is derived 
from Magnesia, in Asia Minor, where the lodestone was 
found in large quantities ; while a third theory finds the 
origin in the Latin word magnus, heavy, on account of the 
heavy nature of the lodestone. The word lodestone itself 
comes from the Saxon laeden , meaning to lead. 

It is fairly certain that the Chinese knew of the lode¬ 
stone long before Greek and Roman times, and according 
to ancient Chinese records this knowledge extends as far 

o 

back as 2600 b.c. Humboldt, in his Cosmos , states that a 

44 


Magnets and Magnetism 

miniature figure of a man which always turned to the south 
was used by the Chinese to guide their caravans across the 
plains of Tartary as early as 1000 b.c. The ancient Greek 
and Roman writers frequently refer to the lodestone. 
Thales, of whom we spoke in Chapter I., believed that its 
mysterious power was due to the possession of a soul, and 
the Roman poet Claudian imagined that iron was a food 
for which the lodestone was hungry. Our limited space 
will not allow of an account of the many curious specula¬ 
tions to which the lodestone has given rise, but the follow¬ 
ing suggestion of one Famianus Strada, quoted from 
Houston’s Electricity in Every-Day Life , is really too 
good to be omitted. 

“ Let there be two needles provided of an equal Length 
and Bigness, being both of them touched by the same 
lodestone ; let the Letters of the Alphabet be placed on the 
Circles on which they are moved, as the Points of the 
Compass under the needle of the Mariner’s Chart. Let 
the Friend that is to travel take one of these with him, first 
agreeing upon the Days and Hours wherein they should 
confer together; at which times, if one of them move the 
Needle, the other Needle, by Sympathy, will move unto 
the same letter in the other instantly, though they are 
never so far distant; and thus, by several Motions of the 
Needle to the Letters, they may easily make up any Words 
or Sense which they have a mind to express.” This is 
wireless telegraphy in good earnest! 

The lodestone is a natural magnet. If we rub a piece 
of steel with a lodestone we find that it acquires the same 
properties as the latter, and in this way we are able to 
make any number of magnets, for the lodestone does not 
lose any of its own magnetism in the process. Such 
magnets are called artificial magnets. Iron is easier to 
magnetize than steel, but it soon loses its magnetism, 

45 


Electricity 

whereas steel retains it; and the harder the steel the better 
it keeps its magnetism. Artificial magnets, therefore, are 
made of specially hardened steel. In this chapter we shall 
refer only to steel magnets, as they are much more con¬ 
venient to use than the lodestone, but it should be 
remembered that both act in exactly the same way. We 

will suppose that we have a pair of bar magnets, and a 

horse-shoe magnet, as shown in Fig. 13. 

If we roll a bar magnet amongst iron filings we find 

that the filings remain 
clinging to it in two 
tufts, one at each 
end, and that few or 
none adhere to the 
middle. These two 
points towards which 
the filings are at¬ 
tracted are called the 
poles of the magnet. 
Each pole attracts 
filings or ordinary 
needles, and one or 
two experiments will 
show that the attrac¬ 
tion becomes evident while the magnet is still some little 
distance away. If, however, we test our magnet with other 
substances, such as wood, glass, paper, brass, etc., we see 
that there is no attraction whatever. 

If one of our bar magnets is suspended in a sort of 
stirrup of copper wire attached to a thread, it comes to rest 
in a north and south direction, and it will be noticed that 
the end which points to the north is marked, either with a 
letter N or in some other way. This is the north pole of 
the magnet, and of course the other is the south pole. If 

46 









































































Magnets and Magnetism 

now we take our other magnet and bring its north pole 
near each pole of the suspended magnet in turn, we find 
that it repels the other north pole, but attracts the south 
pole. Similarly, if we present the south pole, it repels the 
other south pole, but attracts the north pole. From these 
experiments we learn that both poles of a magnet attract 
filings or needles, and that in the case of two magnets 
unlike poles attract, but similar poles repel one another. 
It will be noticed that this corresponds closely with the 
' results of our experiments in Chapter I., which showed 
that an electrified body attracts unelectrified bodies, such 
as bits of paper or pith balls, and that unlike charges 
attract, and similar charges repel each other. So far as we 
have seen, however, a magnet attracts only iron or steel, 
whereas an electrified body attracts any light substance. 
As a matter of fact, certain other substances, such as nickel 
and cobalt, are attracted by a magnet, but not so readily as 
iron and steel; while bismuth, antimony, phosphorus, and 
a few other substances are feebly repelled. 

The simplest method of magnetizing a piece of steel by 
means of one of our bar magnets is the following : Lay the 
steel on the table, and draw one pole of the magnet along 
it from end to end ; lift the magnet clear of the steel, and 
repeat the process several times, always starting at the 
same end and treating each surface of the steel in turn. A 
thin, flat bar of steel is the best for the purpose, but steel 
knitting needles may be made in this way into useful 
experimental magnets. 

We have seen that a magnet has two poles or points 
where the magnetism is strongest. It might be thought 
that by breaking a bar magnet in the middle we should get 
two small bars each with a single pole, but this is not the 
case, for the two poles are inseparable. However many 
pieces we break a magnet into, each piece is a perfect 

47 


Electricity 

magnet having a north and south pole. Thus while we 
can isolate a positive or a negative charge of electricity, we 
cannot isolate north or south magnetism. 

If we place the north pole of a bar magnet near to, but 
not touching, a bar of soft iron, as in Plate II. a , we find that 
the latter becomes a magnet, as shown by its ability to 
support filings ; and that as soon as the magnet is removed 
the filings drop off, showing that the iron has lost its 
magnetism. If the iron is tested while the magnet is in 
position it is found to have a south pole at the end nearer 
the magnet, and a north pole at the end farther away ; and 
if the magnet is reversed, so as to bring its south pole 
nearer the iron, the poles of the latter are found to reverse 
also. The iron has gained its new properties by magnetic 
induction, and we cannot fail to notice the similarity between 
this experiment and that in Fig. 2, Chapter II., which 
showed electro-static induction. A positively or a nega¬ 
tively electrified body induces an opposite charge at the 
nearer end, and a similar charge at the further end of a 
conductor, and a north or a south pole of a magnet 
induces opposite polarity at the nearer end, and a 
similar polarity at the further end of a bar of iron. In 
Chapter II. we showed that the attraction of a pith ball 
by an electrified body was due to induction, and from what 
we have just learnt about magnetic induction the reader 
will have no difficulty in understanding why a magnet 
attracts filings or needles. 

Any one who experiments with magnets must be struck 
with the distance at which one magnet can influence filings 
or another magnet. If a layer of iron filings is spread on a 
sheet of paper, and a magnet brought gradually nearer 
from above, the filings soon begin to move about restlessly, 
and when the magnet comes close enough they fly up to it 
as if pulled by invisible strings. A still more striking 

48^ 


plate rr 


( 



( a ) EXPERIMENT TO SHOW MAGNETIC INDUCTION. 



(b) EXPERIMENT TO SHOW THE PRODUCTION OF MAGNETISM BY AN 

ELECTRIC CURRENT. 





























































Magnets and Magnetism 

experiment consists in spreading filings thinly over a sheet 
of cardboard and moving a magnet to and fro underneath 
the sheet. The result is most amusing. The filings seem 
to stand up on their hind legs, and they march about like 
regiments of soldiers. Here again invisible strings are 
su gg es ted, and we might wonder whether there really is 
anything of the kind. Yes, there is. To put the matter 
in the simplest way, the magnet acts by means of strings 
or lines of force, which emerge from it in definite directions, 
and in a most interesting way we can see some of these 
lines of force actually at work. 

Place a magnet, or any arrangement of magnets, under¬ 
neath a sheet of glass, and sprinkle iron filings from a 
muslin bag thinly and evenly all over the glass. Then tap 
the glass gently with a pencil, and the filings at once 
arrange themselves in a most remarkable manner. All the 
filings become magnetized by induction, and when the tap 
sets them free for an instant from the friction of the glass 
they take up definite positions under the influence of the 
force acting upon them. In this way we get a map of 
the general direction of the magnetic lines of force, which 
are our invisible strings. 

Many different maps may be made in this way, but we 
have space for only two. Plate 111 . a shows the lines of two 
opposite poles. Notice how they appear to stream across 
from one pole to the other. It is believed that there is a 
tension along the lines of force not unlike that in stretched 
elastic bands, and if this is so it is easy to see from the 
figure why opposite poles attract each other. 

Plate III. b shows the lines of force of two similar poles. 
In this case they do not stream from pole to pole, but turn 
aside as if repelling one another, and from this figure we 
see why there is repulsion between two similar poles. It 
can be shown, although in a much less simple manner, that 
D 49 


Electricity 

lines of electric force proceed from electrified bodies, and 
in electric attraction and repulsion between two charged 
bodies the lines of force take paths which closely resemble 
those in our two figures. A space filled with lines of 
magnetic force is called a magnetic field , and one filled 
with lines of electric force is called an electric field. 

A horse-shoe magnet, which is simply a bar of steel 
bent into the shape of a horse-shoe before being mag¬ 
netized, gradually loses its magnetism if left with its poles 
unprotected, but this loss is prevented if the poles are 
connected by a piece of soft iron. The same loss occurs 
with a bar magnet, but as the two poles cannot be connected 
in this way it is customary to keep two bar magnets side 
by side, separated by a strip of wood ; with opposite poles 
together and a piece of soft iron across the ends. Such 
pieces of iron are called keepers , and Fig. 13 shows a 
horse-shoe magnet and a pair of bar magnets with their 
keepers. It may be remarked that a magnet never should 
be knocked or allowed to fall, as rough usage of this kind 
causes it to lose a considerable amount of its magnetism. 
A magnet is injured also by allowing the keeper to slam on 
to it; but pulling the keeper off vigorously does good 
instead of harm. 

If a magnetized needle is suspended so that it is free to 
swing either horizontally or vertically, it not only comes 
to rest in a north and south direction, but also it tilts with 
its north-pointing end downwards. If the needle were 
taken to a place south of the equator it would still tilt, but 
the south-pointing end would be downwards. In both 
cases the angle the needle makes with the horizontal is 
called the magnetic dip. 

It is evident that a suspended magnetized needle would 
not invariably come to rest pointing north and south unless 
it were compelled to do so, and a little consideration shows 

50 


PLATE III 



(ft) LINES OF MAGNETIC FORCE OF TWO OPPOSITE POLES. 



(b) LINES OF MAGNETIC FORCE OF TWO SIMILAR POLES. 








Magnets and Magnetism 

that the needle acts as if it were under the influence of a 
magnet. Dr. Gilbert of Colchester, of whom we spoke in 
Chapter I., gave a great deal of time to the study of 
magnetic phenomena, and in 1600 he announced what may 
be regarded as his greatest discovery: The terrestrial 
globe itself is a great magnet. Here, then, is the explanation 
of the behaviour of the magnetized needle. The Earth 
itself is a great magnet, having its poles near to the 
geographical north and south poles. But a question at 
once suggests itself: “ Since similar poles repel one another, 
how is it that the north pole of a magnet turns towards the 
north magnetic pole of the earth ? ” This apparent diffi¬ 
culty is caused by a confusion in terms. If the Earth’s 
north magnetic pole really has north magnetism, then the 
north-pointing end of a magnet must be a south pole; and 
on the other hand, if the north-pointing end of a magnet 
has north magnetism, then the Earth’s north magnetic pole 
must be really a south pole. It is a troublesome matter to 
settle, but it is now customary to regard the Earth’s north 
magnetic pole as possessing south magnetism, and the 
south magnetic pole as possessing north magnetism. In 
this way the north-pointing pole of a magnet may be looked 
upon as a true north pole, and the south-pointing pole as a 
true south pole. 

Magnetic dip also is seen to be a natural result of the 
Earth’s magnetic influence. Here in England, for instance, 
the north magnetic pole is much nearer than the south 
magnetic pole, and consequently its influence is the 
stronger. Therefore a magnetized needle, if free to do 
so, dips downwards towards the north. At any place 
where the south magnetic pole is the nearer the direction 
of the dip of course is reversed. If placed immediately 
over either magnetic pole the needle would take up a 
vertical position, and at the magnetic equator it would not 

5i 


/ 


Electricity 

dip at all, for the influence of the two magnetic poles would 
be equal. A little study of Fig. 14, which represents a 
dipping needle at different parts of the earth, will make 
this matter clearer. N and S represent the Earth’s north 
and south magnetic poles, and the arrow heads are the 
north poles of the needles. 

Since the Earth is a magnet, we should expect it to 
be able to induce magnetism in a bar of iron, just as our 
artificial magnets do, and we can show that this is actually 
the case. If a steel poker is held pointing to and dipping 

down towards the 
north, and struck 
sharply with a piece 
of wood while in this 
position, it acquires 
magnetic properties 
which can be tested 
by means of a small 
compass needle. It 
is an interesting fact 
that iron pillars and 
railings which have 
been standing for a 
long time in one position are found to be magnetized. 
In the northern hemisphere the bases of upright iron 
pillars are north poles, and their upper ends south poles, 
and in the southern hemisphere the polarity is reversed. 

The most valuable application of the magnetic needle 
is in the compass. An ordinary pocket compass for inland 
use consists simply of a single magnetized needle pivoted 
so as to swing freely over a card on which are marked the 
thirty-two points of the compass. Ships’ compasses are 
much more elaborate. As a rule a compound needle is 
used, consisting of eight slender strips of steel, magnetized 

52 



Fig. 14.—Diagram to illustrate Magnetic Dip. 




Magnets and Magnetism 

separately, and suspended side by side. A compound 
needle of this kind is very much more reliable than a 
single needle. The material of which the card is made 
depends upon whether the illumination for night work is 
to come from above or below. If the latter, the card must 
be transparent, and it is often made of thin sheet mica; 
but if the light comes from above, the card is made of 
some opaque material, such as very stout paper. The 
needle and card are contained in a sort of bowl made of 
copper. In order to keep this bowl in a horizontal position, 
however the ship may be pitching and rolling, it is sup¬ 
ported on gimbals, which are two concentric rings attached 
to horizontal pivots, and moving in axes at right angles 
to one another. Further stability may be obtained by 
weighting the bottom of the bowl with lead. There are 
also liquid compasses, in which the card is floated on the 
surface of dilute alcohol, and many modern ships’ com¬ 
passes have their movements regulated by a gyrostat. 

The large amount of iron and steel used in the con¬ 
struction of modern vessels has a considerable effect upon 
the compass needle, and unless the compass is protected 
from this influence its readings are liable to serious errors. 
The most satisfactory way of giving this protection is by 
placing on each side of the compass a large globe of soft 
iron, twelve or more inches in diameter. 

On account of the fact that the magnetic poles of the 
Earth do not coincide with the geographical north and 
south poles, a compass needle seldom points exactly north 
and south, and the angle between the magnetic meridian 
and the geographical meridian is called the declination. 
The discovery that the declination varies in different parts 
of the world was made by Columbus in 1492. For pur¬ 
poses of navigation it is obviously very important that the 
declination at all points of the Earth’s surface should be 

53 


Electricity 

known, and special magnetic maps are prepared in which 
all places having the same declination are joined by a 
line. 

It is an interesting fact that the Earth’s magnetism is 
subject to variation. The declination and the dip slowly 
change through long periods of years, and there are also 
slight annual and even daily variations. 

At one time magnets were credited with extraordinary 
effects upon the human body. Small doses of lodestone, 
ground to powder and mixed with water, were supposed 
to prolong life, and Paracelsus, a famous alchemist and 
physician, born in Switzerland in 1493, believed in the 
potency of lodestone ointment for wounds made with steel 
weapons. Baron Reichenbach, 1788-1860, believed that 
he had discovered the existence of a peculiar physical force 
closely connected with magnetism, and he gave this force 
the name Od. It was supposed to exist everywhere, 
and, like magnetism, to have two poles, positive and 
negative ; the left side of the body being od-positive, and 
the right side od-negative. Certain individuals, known as 
“ sensitives,” were said to be specially open to its influence. 
These people stated that they saw strange flickering lights 
at the poles of magnets, and that they experienced peculiar 
sensations when a magnet was passed over them. Some 
of them indeed were unable to sleep on the left side, be¬ 
cause the north pole of the Earth, being od-negative, had 
a bad effect on the od-negative left side. The pretended 
revelations of these “sensitives ” created a great stir at the 
time, but now nobody believes in the existence of Od. 

Professor Tyndall was once invited to a seance, with 
the object of convincing him of the genuineness of spiritual¬ 
ism. He sat beside a young lady who claimed to have 
spiritualistic powers, and his record of his conversation with 
her is amusing. The Reichenbach craze was in full swing 

54 


Magnets and Magnetism 

at the time, and Tyndall asked if the lady could see any of 
the weird lights supposed to be visible to “sensitives.” 

“ Medium. —Oh yes; but I see the light around all 
bodies. 

/.—Even in perfect darkness ? 

Medium. —Yes; I see luminous atmospheres round 
all people. The atmosphere which surrounds 
Mr. R. C. would fill this room with light. 

/.—You are aware of the effects ascribed by Baron 
Reichenbach to magnets ? 

Medium. —Yes ; but a magnet makes me terribly ill. 

I .—Am I to understand that, if this room were 
perfectly dark, you could tell whether it con¬ 
tained a magnet, without being informed of 
the fact ? 

Medium. —I should know of its presence on enter¬ 
ing the room. 

/.-How? 

Medium. —I should be rendered instantly ill. 

I .—How do you feel to-day? 

Medium. —Particularly well; I have not been so 
well for months. 

/.—Then, may I ask you whether there is, at the 
present moment, a magnet in my possession ? 

The young lady looked at me, blushed, and 
stammered, ‘No; I am not en rapport with 
you.’ 

/ sat at her right hand\ and a left-hand pocket , 
within six inches of her person , contained a 
magnet .” 

Tyndall adds, “Our host here deprecated discussion 
as it ‘exhausted the medium.’” 


55 


CHAPTER VII 


THE PRODUCTION OF MAGNETISM BY 

ELECTRICITY 

In the previous chapter attention was drawn to the fact 
that there are many close parallels between electric and 
magnetic phenomena, and in this chapter it will be shown 
that magnetism can be produced by electricity. In the 



A B 


Fig. 15.—Diagram to illustrate Magnetic effect of an Electric Current. 

year 1819 Professor Oersted, of the University of Copen¬ 
hagen, discovered that a freely swinging magnetized needle, 
such as a compass needle, was deflected by a current of 
electricity flowing through a wire. In Fig. 15, A, a 
magnetic needle is shown at rest in its usual north and 
south direction, and over it is held a copper wire, also 
pointing north and south. A current of electricity is now 
sent through the wire, and the needle is at once deflected, 
Fig. 15, B. The direction of the current is indicated by 

56 













Production of Magnetism by Electricity 

an arrow, and the direction in which the needle has moved 
is shown by the two small arrows. If the direction of the 
current is reversed, the needle will be deflected in the 
opposite direction. From this experiment we see that the 
current has brought magnetic influences into play, or in 
other words has produced magnetism. If iron filings are 
brought near the wire while the current is flowing, they 
are at once attracted and cling to the wire, but as soon as 
the current is stopped 
they drop off. This 
shows us that the wire 
itself becomes a magnet 
during the passage of 
the current, and that it 
loses its magnetism 
when the current ceases 
to flow. 

Further, it can be 
shown that two freely 
moving parallel wires 
conveying currents at¬ 
tract or repel one 
another according to 
the direction of the cur¬ 
rents. If both currents are flowing in the same direction 
the wires attract one another, but if the currents flow in 
opposite directions the wires repel each other. Fig. 16 
shows the direction of the lines of force of a wire conveying 
a current and passed through a horizontal piece of cardboard 
covered with a thin layer of iron filings ; and from this 
figure it is evident that the passage of the current produces 
what we may call magnetic whirls round the wire. 

A spiral of insulated wire through which a current is 
flowing shows all the properties of a magnet, and if free to 

5 7 



Fig. 16.—Magnetic Field round wire 
conveying a Current. 







Electricity 

move it comes to rest pointing north and south. It is 
attracted or repelled by an ordinary magnet according to 
the pole presented to it and the direction of the current, 
and two such spirals show mutual attraction and repulsion. 
A spiral of this kind is called a solenoid, and in addition 
to the properties already mentioned it has the peculiar 
power of drawing or sucking into its interior a rod of 
iron. Solenoids have various practical applications, and in 
later chapters we shall refer to them again. 

If several turns of cotton-covered wire are wound round 
an iron rod, the passing of a current through the wire 
makes the rod into a magnet (Plate II. b ), but the magnet¬ 
ism disappears as soon as the current ceases to flow. A 
magnet made by the passage of an electric current is called 
an electro-magnet, and it has all the properties of the 
magnets mentioned in the previous chapter. A bar of steel 
may be magnetized in the same way, but unlike the iron 
rod it retains its magnetism after the current is interrupted. 
This provides us with a means of magnetizing a piece of 
steel much more strongly than is possible by rubbing with 
another magnet. Steel magnets, which retain their 
magnetism, are called permanent magnets, as distin¬ 
guished from electro-magnets in which soft iron is used, so 
that their magnetism lasts only as long as the current 
flows. 

Electro-magnets play an extremely important part in 
the harnessing of electricity; in fact they are used in one 
form or another in almost every kind of electrical 
mechanism. In later chapters many of these uses will be 
described, and here we will mention only the use of 
electro-magnets for lifting purposes. In large engineer¬ 
ing works powerful electro-magnets, suspended from some 
sort of travelling crane, are most useful for picking up and 
carrying about heavy masses of metal, such as large 


Production of Magnetism by Electricity 

castings. No time is lost in attaching the casting to the 
crane; the magnet picks it up directly the current is 
switched on, and lets it go the instant the current is 
stopped. In any large steel works the amount of scrap 
material produced is astonishingly great, hundreds of tons 
of turnings and similar scrap accumulating in a very short 
time. A huge mound of turnings is awkward to deal with 
by ordinary manual labour, but a combination of electro¬ 
magnet and crane solves the difficulty completely, lifting 
and loading the scrap into carts or trucks at considerable 
speed, and without requiring much attention. 

Some time ago a disastrous fire occurred at an 
engineering works in the Midlands, the place being almost 
entirely burnt out. Amongst the debris was, of course, a 
large amount of metal, and as this was too valuable to be 
wasted, an electro-magnet was set to work on the wreckage. 
The larger pieces of metal were picked up in the ordinary 
way, and then the remaining rubbish was shovelled against 
the face of the magnet, which held on to the metal but 
dropped everything else, and in this way some tons of 
metal were recovered. 

The effect produced upon a magnetized needle by a 
current of electricity affords a simple means of detecting the 
existence of such a current. An ordinary pocket compass 
can be made to show the presence of a moderate current, but 
for the detection of extremely small currents a much more 
sensitive apparatus is employed. This is called & galvano¬ 
meter, and in its simplest form it consists essentially of 
a delicately poised magnetic needle placed in the middle of 
a coil of several turns of wire. The current thus passes 
many times round the needle, and this has the effect of 
greatly increasing the deflection of the needle, and hence 
the sensitiveness of the instrument. Although such an 
arrangement is generally called a galvanometer, it is really 

59 


Electricity 

a galvanoscope, for it does not measure the current but only 
shows its presence. 

We have seen that electro-motive force is measured in 
volts, and that the definition of a volt is that electro-motive 
force which will cause a current of one ampere to flow 
through a conductor having a resistance of one ohm. If we 
make a galvanometer with a long coil of very thin wire 
having a high resistance, the amount of current that will 
flow through it will be proportionate to the electro-motive 
force. Such a galvanometer, fitted with a carefully 
graduated scale, in this way will indicate the number of 
volts, and it is called a voltmeter. If we have a galvano¬ 
meter with a short coil of very thick wire, the resistance put 
in the way of the current is so small that it may be left out 
of account, and by means of a graduated scale the number 
of amperes may be shown ; such an instrument being called 
an amperemeter , or ammeter. 

For making exact measurements of electric currents the 
instruments just described are not suitable, as they are not 
sufficiently accurate ; but their working shows the principle 
upon which currents are measured. The actual instruments 
used in electrical engineering and in scientific work are 
unfortunately too complicated to be described here. 


60 


CHAPTER VIII 


THE INDUCTION COIL 

The voltaic cell and the accumulator provide us with 
currents of electricity of considerable volume, but at low 
pressure or voltage. For many purposes, however, we re¬ 
quire a comparatively small amount of current at very high 
pressure, and in such cases we use an apparatus called 
the induction coil. Just as an electrified body and a 
magnet will induce electrification and magnetism respec¬ 
tively, so a current of electricity will induce another current ; 
and an induction coil is simply an arrangement by which a 
current in one coil of wire is made to induce a current in 
another coil. 

Suppose we have two coils of wire placed close to¬ 
gether, one connected to a battery of voltaic cells, with 
some arrangement for starting and stopping the current 
suddenly, and the other to a galvanometer. As soon as 
we send the current through the first coil, the needle of 
the galvanometer moves, showing that there is a current 
flowing through the second coil; but the needle quickly 
comes back to its original position, showing that this 
current was only momentary. So long as we keep the 
current flowing through the first coil the galvanometer 
shows no further movement, but as soon as we stop the 
current the needle again shows by its movements that 
another momentary current has been produced in the 
second coil. This experiment shows us that a current 

61 


Electricity 

induces another current only at the instant it is started or 
stopped, or, as we say, at the instant of making or breaking 
the circuit. 

The coil through which we send the battery current is 
called the “primary coil,” and the one in which a current is 
induced is called the “ secondary coil.” The two momentary 
currents in the secondary coil do not both flow in the same 
direction. The current induced on making the circuit 
flows in a direction opposite to that of the current in the 
primary coil; and the current induced on breaking the 
circuit flows in the same direction as that in the primary 
coil. If the two coils are exactly alike, the induced current 
will have the same voltage as the primary current; but 
if the secondary coil has twice as many turns of wire 
as the primary coil, the induced current will have twice 
the voltage of the primary current. In this way, by 
multiplying the turns of wire in the secondary coil, we 
can go on increasing the voltage of the induced current, 
and this is the principle upon which the induction coil 
works. 

We may now describe the construction of such a coil. 
The primary coil is made of a few turns of thick copper 
wire carefully insulated, and inside it is placed a core con¬ 
sisting of a bundle of separate wires of soft iron. Upon 
this coil, but carefully insulated from it, is wound the 
secondary coil, consisting of a great number of turns of 
very fine wire. In large induction coils the secondary coil 
has thousands of times as many turns as the primary, and 
the wire forming it may be more than a hundred miles in 
length. The ends of the secondary coil are brought to 
terminals so that they can be connected up to any apparatus 
as desired. 

In order that the induced currents shall follow each 
other in quick succession, some means of rapidly making 

62 


The Induction Coil 

and breaking the circuit is required, and this is provided 
by an automatic contact breaker. It consists of a small 
piece of soft iron, A, Fig. 17, fixed to a spring, B, having 
a platinum tip at C. The adjustable screw, D, also has a 
platinum tip, E. Normally the two platinum tips are just 
touching one another, and matters are arranged so that 
their contact completes the circuit. When the apparatus 
is connected to a suitable battery a current flows through 
the primary coil, and the iron core, F, becomes an electro¬ 
magnet, which draws A towards it. The platinum tips 
are thus no longer in contact and the circuit is broken. 
Immediately this occurs the 
iron core loses its magnetism 
and ceases to attract A, which 
is then moved back again by 
the spring B, so that the 
platinum tips touch, the circuit 


i 



6 


is once more completed, and p f — 
the process begins over again. ^ 6 
All this takes place with the 
utmost rapidity, and the speed 

at which the contact-breaker 

works is SO great as to pro- F ^ G - 1 7-—Diagram showing working 
. & r Contact-Breaker for Induction Coil. 

duce a musical note. There 

are many other types of contact-breakers, but in every 
case the purpose is the same, namely, to make and 
break the primary circuit as rapidly as possible. 

The efficiency of the coil is greatly increased by a 
condenser which is inserted in the primary circuit. It 
consists of alternate layers of tinfoil and paraffined 
paper, and its action is like that of a Leyden jar. 
A switch is provided to turn the battery current on or 
off, and there is also a reversing switch or commutator, 
by means of which the direction of the current may be 

63 



























Electricity 

reversed. The whole arrangement is mounted on a 
suitable wooden base, and its general appearance is shown 
in Fig. 18. 

By means of a large induction coil we can obtain a 
voltage hundreds or even thousands of times greater than 
that of the original battery current, but on account of the 
great resistance of a very long, thin wire, the amperage is 
much smaller. The induction coil produces a rapid 
succession of sparks, similar to those obtained from a 
Wimshurst machine. A coil has been constructed capable 



By permission o/] [Harry IV. Cox , Ltd. 


Fig. 18.— Typical Induction Coil. 


of giving sparks 42^ inches in length, and having a 
secondary coil with 340,000 turns of wire, the total 
length of the wire being 280 miles. Induction coils are 
largely employed for scientific purposes, and they are 
used in wireless telegraphy and in the production of 
X-rays. 

The principle of the induction coil can be applied 
also to the lowering of the voltage of a current. If 
we make the secondary coil with less, instead of more 
turns of wire than the primary coil, the induced current 
will be of lower voltage than the primary current, but 

64 




























The Induction Coil 

its amperage will be correspondingly higher. This fact 
is taken advantage of in cases where it is desirable 
to transform a high voltage current from the public 
mains down to a lower voltage current of greater 
amperage. 


E 


65 


CHAPTER IX 


THE DYNAMO AND THE ELECTRIC MOTOR 

Most of my readers will have seen the small working 
models of electric tramcars which can be bought at any 
electrical supply stores. These usually require a current of 
about one ampere at three or four volts. If we connect 
such a car to the battery recommended for it, and keep it 
running continuously, we find that the battery soon begins 
to show signs of exhaustion. Now if we imagine our 
little car increased to the size of an electric street car, and 
further imagine, say, a hundred such cars carrying heavy 
loads day after day from morning to night, we shall realize 
that a battery of cells capable of supplying the current 
necessary to run these cars would be so colossal as to be 
utterly impracticable. We therefore must look beyond the 
voltaic cell for a source of current for such a purpose, and 
this source we find in a machine called the “ dynamo,” 
from the Greek word dynamis , meaning force. 

Oersted’s discovery of the production of magnetism by 
electricity naturally suggested the possibility of producing 
electricity from magnetism. In the year 1831 one of the 
most brilliant of our British scientists, Michael Faraday, 
discovered that a current of electricity could be induced in 
a coil of wire either by moving the coil towards or away 
from a magnet, or by moving a magnet towards or away 
from the coil, v This may be shown in a simple way by 
connecting the ends of a coil of insulated wire to a galvano- 

66 


The Dynamo and the Electric Motor 

meter, and moving a bar magnet in and out of the coil; 
when the galvanometer shows that a current is induced in 
the coil on the insertion of the magnet, and again on its 
withdrawal. We have seen that a magnet is surrounded 
by a field of magnetic force, and Faraday found that the 
current was induced when the lines of force were cut across. 

Utilizing this discovery Faraday constructed the first 
dynamo, which consisted of a copper plate or disc rotated 
between the poles of a powerful horse-shoe magnet, so as 
to cut the lines of force. The current flowed either from 
the shaft to the rim, or vice versa , according to the direction 
of rotation ; and it was conducted away by means of two 
wires with spring contacts, one pressing against the shaft, 
and the other against the circumference of the disc. This 
machine was miserably inefficient, but it was the very first 
dynamo, and from it have been slowly evolved the mighty 
dynamos used to-day in electric power stations through¬ 
out the world. There is a little story told of Faraday 
which is worth repeating even if it is not true. Speaking 
of his discovery that a magnet could be made to produce 
an electric current, a lady once said to him, “ This is all 
very interesting, but what is the use of it?” “Madam,” 
replied Faraday, “what is the use of a baby?” In 
Faraday’s “baby” dynamo, as in all others, some kind of 
power must be used to produce the necessary motion, so 
that all dynamos are really machines for converting 
mechanical energy into electrical energy. 

The copper disc in this first dynamo did not prove 
satisfactory, and Faraday soon substituted for it rotating 
coils of wire. In 1832 a dynamo was constructed in which 
a length of insulated wire was wound upon two bobbins 
having soft iron cores, and a powerful horse-shoe magnet 
was fixed to a rotating spindle in such a position that its 

poles faced the cores of the bobbins. This machine gave 

67 


Electricity 

a fair current, but it was found that the magnet gradually 
lost its magnetism on account of the vibration caused by 
its rotation. The next step was to make the magnet a 
fixture, and to rotate the bobbins of wire. This was a 
great improvement, and the power of machines built on 
this principle was much increased by having a number of 
rotating coils and several magnets. One such machine 

had 64 separate 
coils rotating 
between the 
poles of 40 large 
magnets. Fin- 

o 

ally, permanent 
magnets were 
superseded by 
3 electro - mag¬ 
net s, which 
gave a much 
more powerful 
field of force. 

Having seen 
something of 
the underlying 
principle and of 
the history of 
the dynamo, we 
must turn our attention to its actual working. Fig. 19 is a 
rough representation of a dynamo in its simplest form. The 
two poles of the magnet are shown marked north and south, 
and between them revolves the coil of wire A 1 A 2 , mounted 
on a spindle SS. This revolving coil is called the armature. 
To each of the insulated rings RR is fixed one end of the 
coil, and BB are two brushes of copper or carbon, one 
pressing on each ring. From these brushes the current is 

68 



Fig. 19.—Diagram showing principle of Dynamo 
producing Alternating Current. 


















The Dynamo and the Electric Motor 

led away into the main circuit, and in this case we may 
suppose that the current is used to light a lamp. 

In speaking of the induction coil we saw that the 
currents induced on making and on breaking the circuit 
flowed in opposite directions, and similarly, Faraday found 
that the currents induced in a coil of wire on inserting and 
on withdrawing his magnet flowed in opposite directions. 
In the present case the magnet is stationary and the coil 
moves, but the effect is just the same. Now if we suppose 
the armature to be revolving in a clockwise direction, then 
A 1 is descending and entering the magnetic field in front of 
the north pole, consequently a current is induced in the 
coil, and of course in the main circuit also, in one direction. 
Continuing its course, A 1 passes away from this portion of 
the magnetic field, and thus a current is induced in the 
opposite direction. In this way we get a current which 
reverses its direction every half-revolution, and such a 
current is called an alternating current. If, as in our 
diagram, there are only two magnetic poles, the current 
flows backwards and forwards once every revolution, but 
by using a number of magnets, arranged so that the coil 
passes in turn the poles of each, it can be made to flow 
backwards and forwards several times. One complete 
flow backwards and forwards is called a period, and the 
number of periods per second is called the periodicity or 
frequency of the current. A dynamo with one coil or set 
of coils gives what is called “ single-phase ” current, that is, a 
current having one wave which keeps flowing backwards 
and forwards. If there are two distinct sets of coils we get 
a two-phase current, in which there are two separate waves, 
one rising as the other falls. Similarly, by using more 
sets of coils, we may obtain three-phase or polyphase 
currents. 

Alternating current is unsuitable for certain purposes, 

69 


Electricity 

such as electro-plating ; and by making a small alteration in 
our dynamo we get a continuous or direct current, which 
does not reverse its direction. Fig. 20 shows the new 
arrangement. Instead of the two rings in Fig. T9, we have 
now a single ring divided into two parts, each half being 
connected to one end of the revolving coil. Each brush, 
therefore, remains on one portion of the ring for half a 

revolution, and 
then passes 
over on to the 
other portion. 
During one 
half - revolution 
we will suppose 
the current to 
be flowing from 
5 brush B 1 in the 
direction of the 
lamp. Then 
during the next 
half - revolution 
the current 
flows in the op- 
positedirection; 
but brush B 1 
has passed on 
to the other half 
of the ring, and so the current is still leaving by it. 
In this way the current must always flow in the same 
direction in the main circuit, leaving by brush B 1 and 
returning by brush B 2 . This arrangement for making the 
alternating current into a continuous current is called a 
commutator. 

In actual practice a dynamo has a set of electro-magnets, 

70 



Fig. 20.—Diagram showing principle of Dynamo 
producing Continuous Current. 














PLATE I\ 



Tty permission 0/ 


Lancashire Dynamo &• Motor Co. Ltd. 


A TYPICAL DYNAMO AND ITS PARTS. 



















The Dynamo and the Electric Motor 

and the armature consists of many coils of wire mounted 
on a core of iron, which has the effect of concentrating the 
lines of force. The armature generally revolves in small 
dynamos, but in large ones it is usually a fixture, while the 
electro-magnets revolve. Plate IV. shows a typical dynamo 
and its parts. 

As we saw in an earlier chapter, an electro-magnet has 
magnetic powers only while a current is being passed 
through its winding, and so some means of supplying 
current to the electro-magnets in a dynamo must be pro¬ 
vided. It is a remarkable fact that it is almost impossible 
to obtain a piece of iron which has not some traces of 
magnetism, and so when a dynamo is first set up there is 
often sufficient magnetism in the iron of the electro-magnets 
to produce a very weak field. The rapid cutting of the 
feeble lines of force of this field sets up a weak current, 
which, acting upon the electro-magnets, gradually brings 
them up to full strength. Once the dynamo is generating 
current it keeps on feeding its magnets by sending either 
the whole or a part of its current through them. After 
it has once been set going the dynamo is always able to 
start again, because the magnet cores retain enough 
magnetism to set up a weak field. If there is not enough 
magnetism in the cores to start a. dynamo for the first 
time, a current from some outside source is sent round the 
magnets. 

The foregoing remarks apply to continuous current 
dynamos only. Alternating current can be used for exciting 
electro-magnets, but in this case the magnetic field produced 
is alternating also, so that each pole of the magnet has 
north and south magnetism alternately. This will not do 
for dynamo field magnets, and therefore an alternating 
current dynamo cannot feed its own magnets. The electro¬ 
magnets in such dynamos are supplied with current from a 

7i 


Electricity 

separate continuous current dynamo, which may be of quite 
small size. 

It is a very interesting fact that electric current can 
be generated by a dynamo in which the earth itself is 
used to provide the magnetic field, no permanent or electro¬ 
magnets being used at all. A simple form of dynamo 
of this kind consists of a rectangular loop of copper wire 
rotating about an axis pointing east and west, so that 
the loop cuts the lines of force of the Earth’s magnetic 
field. 

The dynamo provides us with a constant supply of 
electric current, but this current is no use unless we can 
make it do work for us. If we reverse the usual order of 
things in regard to a dynamo, and supply the machine with 
current instead of mechanical power, we find that the 
armature begins to revolve rapidly, and the machine is 
no longer a dynamo, but has become an electric motor. 
This shows us that an electric motor is simply a dynamo 
reversed. Let us suppose that we wish to use the 
dynamo in Fig. 20 as a motor. In order to supply the 
current we will take away the lamp and substitute a 
second continuous-current dynamo. We know from 
Chapter VII. that when a current is sent through a coil 
of wire the coil becomes a magnet with a north and a 
south pole. The coil in our dynamo becomes a magnet 
as soon as the current is switched on, and the attraction 
between its poles and the opposite poles of the magnet 
causes it to make half a revolution. At this point the 
commutator reverses the current, and consequently the 
polarity of the coil, so that there is now repulsion where 
previously there was attraction, and the coil makes another 
half-revolution. So the process goes on until the armature 
attains a very high speed. In general construction there is 
practically no difference between a dynamo and a motor, 

72 


The Dynamo and the Electric Motor 

but there are differences in detail which adapt each to its 
own particular work. By making certain alterations in 
their construction electric motors can be run with alternating 
current. 

The fact that a dynamo could be reversed and run as a 
motor was known probably as early as 1838, but the great 
value of this reversibility does not seem to have been 
realized until 1873. At an industrial exhibition held at 
Vienna in that year, it so happened that a workman or 
machinery attendant connected two cables to a dynamo 
-which was standing idle, and he was much surprised to 
find that it at once began to revolve at a great speed. It 
was then seen that the cables led to another dynamo which 
was running, and that the current from this source had 
made the first dynamo into a motor. There are many 
versions of this story, but the important point in all 
is that this was the first occasion on which general 
attention was drawn to the possibilities of the electric 
motor. 

The practical advantages afforded by the electric motor 
are many and great. Once we have installed a sufficiently 
powerful dynamo and a steam or other engine to drive it, 
we can place motors just where they are required, either 
close to the dynamo or miles away, driving them simply by 
means of a connecting cable. In factories, motors can be 
placed close to the machines they are required to drive, 
anywhere in the building, thus doing away with all com¬ 
plicated and dangerous systems of shafting and belts. In 
many cases where it would be either utterly impossible or 
at least extremely inconvenient to use any form of steam, 
gas, or oil engine, electric motors can be employed without 
the slightest difficulty. In order to realize this, one only 
has to think of the positions in which electrically-driven 
ventilating fans are placed, or of the unpleasantly familiar 

73 


Electricity 

electric drill of the dentist. An electric motor is small and 
compact, gives off no fumes and practically no heat, makes 
very little noise, is capable of running for very long periods 
at high speed and with the utmost steadiness, and requires 
extremely little attention. 


74 


CHAPTER X 


ELECTRIC POWER STATIONS 

It is apparently a very simple matter to fit up a power 
station with a number of very large dynamos driven by 
powerful engines, and to distribute the current produced by 
these dynamos to all parts of a town or district by means 
of cables, but as a matter of fact it is a fairly complicated 
engineering problem. First of all the source of power for 
driving the dynamos has to be considered. In private and 
other small power plants, gas, petrol or oil engines are 
generally used, but for large stations the choice lies between 
steam and water power. In this country steam power is 
used almost exclusively. Formerly the ordinary reciprocat¬ 
ing steam engines were always employed, and though these 
are still in very extensive use, they are being superseded in 
many cases by steam turbines. The turbine is capable of 
running at higher speeds than the reciprocating engine, and 
at the greatest speeds it runs with a great deal less noise, 
and with practically no vibration at all. More than this, 
turbines take up much less room, and require less oil and 
attendance. The turbines are coupled directly to the 
dynamos, so that the two machines appear almost as one. 
In the power station shown on Plate V. a number of alter¬ 
nating current dynamos coupled to steam turbines are seen. 

A large power station consumes enormous quantities of 
coal, and for convenience of supply it is situated on the 
bank of a river or canal, or, if neither of these is available, 

75 


Electricity 

as close to the railway as possible. The unloading of the 
coal barges or trucks is done mechanically, the coal passing 
into a large receiving hopper. From here it is taken to 
another hopper close to the furnaces by means of coal 
elevators and conveyors, which consist of a number of 
buckets fixed at short intervals on an endless travelling 
chain. From the furnace hopper the coal is fed into the 
furnaces by mechanical stokers, and the resulting ash and 
clinker falls into a pit below the furnaces, from which it is 
carted away. 

The heat produced in the furnaces is used to generate 
steam, and from the boilers the steam passes to the engines 
along a steam pipe. After doing its work in the engines, 
the steam generally passes to a condenser, in which it is 
cooled to water, freed from oil and grease, and returned to 
the boilers to be transformed once more into steam. As 
this water from the condenser is quite warm, less heat is 
required to raise steam from it than would be the case if 
the boiler supply were kept up with cold water. The 
power generated by the engines is used to drive the 
dynamos, and stout copper cables convey the current from 
these to what are called “ bus ” bars. There are two of 
these, one receiving the positive cable from the dynamos, 
and the other the negative cable, and the bars run from end 
to end of a large main switchboard. From this switchboard 
the current is distributed by other cables known as feeders. 

The nature of the current generated at a power station 
is determined to a great extent by the size of the district to 
be supplied. Generally speaking, where the current is not 
to be transmitted beyond a radius of about two miles from 
the station, continuous current is generated ; while alternat¬ 
ing current is employed for the supply of larger areas. In 
some cases both kinds of current are generated at one 
station. 


76 


PLATE V. 



LOTS ROAD ELECTRIC POWER STATION, CHELSEA. 









































































t 




Electric Power Stations 

If continuous current is to be used, it is generated 
usually at a pressure of from 400 to 500 volts, the average 
being about 440 volts ; and the supply is generally on what 
is known as the three-wire system. Three separate wires 
are employed. The two outer wires are connected 
respectively to the positive and the negative bus bars 
running along the main switchboard, these bars receiving 
positive or negative current directly from the dynamos. 
The outer wires therefore carry current at the full voltage 
of the system. Between them is a third and smaller wire, 
connected to a third bar, much smaller than the outer bars, 
and known as the mid-wire bar. This bar is not connected 
to the dynamos, but to earth, by means of a large plate of 
copper sunk into the ground. Connexion between the 
mid-wire bar and the outer bars is made by two machines 
called “ balancers,” one connecting the mid-wire bar and the 
positive bus bar, and the other the mid-wire bar and the 
negative bus bar. If the pressure between the outer bars 
is 440 volts, then the pressure between the mid-wire bar and 
either of the outer bars will be 220 volts, that is just half. 

The balancers serve the purpose of balancing the 
voltage on each side, and they are machines capable of 
acting either as motors or dynamos. In order to comply 
with Board of Trade regulations, electric appliances of all 
kinds intended for ordinary domestic purposes, including 
lamps, and heating and cooking apparatus, are supplied 
with current at a pressure not exceeding 250 volts. In a 
system such as we are describing, all these appliances are 
connected between the mid-wire and one or other of the 
outer wires, thus receiving current at 220 volts. In 
practice it is impossible to arrange matters so that the 
lamps and other appliances connected with the positive side 
of the system shall always take the same amount of current 
as those connected with the negative side, and there is 

77 


Electricity 

always liable to be a much greater load on one side or the 
other. If, for instance, a heavy load is thrown on the 
negative side, the voltage on that side will drop. The 
balancer on the positive side then acts as an electric motor, 
drives the balancer on the negative side as a dynamo, and 
thus provides the current required to raise the voltage on 
the negative side until the balance is restored. The work¬ 
ing of the balancers, which need not be described in further 
detail, is practically automatic. Electric motors, for driving 
electric trams or machinery of any kind, are connected 
between the outer wires, so that they receive the full 440 
volts of the system. 

In any electric supply system the demand for current 
does not remain constant, but fluctuates more or less. For 
instance, in a system including an electric tramway, if a car 
breaks down and remains a fixture for a short time, all cars 
behind it are held up, and a long line of cars is quickly 
formed. When the breakdown is repaired, all the cars 
start practically at the same instant, and consequently a 
sudden and tremendous demand for current is made. In a 
very large tramway system in a fairly level city, the 
fluctuations in the demand for current, apart from accidents, 
are not very serious, for they tend to average themselves ; 
but in a small system, and particularly if the district is hilly, 
the fluctuations are very great, and the current demand 
may vary as much as from 400 to 2000 amperes. Again, 
in a system supplying power and light, the current demand 
rises rapidly as the daylight fails on winter afternoons, 
because, while workshop and other motors are still in full 
swing, thousands of electric lamps are switched on more or 
less at the same time. The power station must be able to 
deal with any exceptional demands which are likely to 
occur, and consequently more current must be available 
than is actually required under average conditions. Instead 

78 


Electric Power Stations 

of having generating machinery large enough to meet all 
unusual demands, the generators at a station using continu¬ 
ous current may be only of sufficient size to supply a little 
more than the average demand, any current beyond this 
being supplied by a battery of storage cells. The battery 
is charged during periods when the demand for current is 
small, and when a heavy load comes on, the current from 
the battery relieves the generators of the sudden strain. 
To be of any service for such a purpose the storage battery 
of course must be very large. Plate VI. shows a large 
battery of no cells, and some idea of the size of the 
individual cells may be obtained from the fact that each 
weighs about 3900 lb. 

Alternating current is produced at almost all power 
stations supplying large districts. It is generated at high 
pressure, from 2000 volts upwards, the highest pressure 
employed in this country being about 11,000 volts. Such 
pressures are of course very much too high for electric 
lamps or motors, and the object of generating current of 
this kind is to secure the greatest economy in transmission 
through the long cables. Electric energy is measured in 
watts, the watts being obtained by multiplying together 
the pressure or voltage of the current, and its rate of flow 
or amperage. From this it will be seen that, providing the 
product of voltage and amperage remains the same, it 
makes no difference, so far as electric energy is concerned, 
whether the current be of high voltage and low amperage, 
or of low voltage and high amperage. Now in trans¬ 
mitting a current through a long cable, there is a certain 
amount of loss due to the heating of the conductor. This 
heating is caused by the current flow, not by the pressure ; 
and the heavier the current, the greater the heating, and 
the greater the loss. This being so, it is clear that by 
decreasing the current flow, and correspondingly increasing 

79 


Electricity 

the pressure, the loss in transmission will be reduced ; and 
this is why alternating current is generated at high pressure 
when it is to be transmitted to a distance. 

The kind of alternating current generated is usually 
that known as three-phase current. Formerly single-phase 
current was in general use, but it has been superseded by 
three-phase current because the latter is more economical 
to generate and to distribute, and also more satisfactory for 
electric motors. The actual voltage of the current sent out 
from the station varies according to the distance to which 
the current is to be conveyed. In the United States and 
in other countries where current has to be conveyed to 
places a hundred or even more miles from the station, 
pressures as high as 120,000 volts are in use. It is possible 
to produce alternating current at such pressures directly 
from the dynamos, but in practice this is never done, on 
account of the great liability to breakdown of the insulation. 
Instead, the current is generated at from 2000 to 10,000 or 
11,000 volts, and raised to the required pressure, before 
leaving the station, by means of a step-up transformer. 
We have seen that an induction coil raises, or steps up, the 
voltage of the current supplied to it. A step-up transformer 
works on the same principle as the induction coil, and in 
passing through it the current is raised in voltage, but 
correspondingly lowered in amperage. Of course, if the 
pressure of the current generated by the dynamos is already 
sufficiently high to meet the local requirements, the trans¬ 
former is not used. 

For town supply the current from the power station is 
led along underground cables to a number of sub-stations, 
situated in different parts of the town, and generally under¬ 
ground. At each sub-station the current passes through a 
step-down transformer, which also acts on the principle of the 
induction coil, but in the reverse way, so that the voltage is 

80 


PLATE YT 




































Electric Power Stations 

lowered instead of being raised. From the transformer the 
current emerges at the pressure required for use, but it is 
still alternating current; and if it is desired to have a 
continuous-current supply this alternating current must be 
converted. One of the simplest arrangements for this 
purpose consists of an electric motor and a dynamo, the 
two being coupled together. The motor is constructed to 
run on the alternating current from the transformer, and 
it drives the dynamo, which is arranged to generate con¬ 
tinuous current. There is also a machine called a “ rotary 
converter,” which is largely used instead of the motor 
generator. This machine does the work of both motor and 
dynamo, but its action is too complicated to be described 
here. From the sub-stations the current, whether con¬ 
verted or not, is distributed as required by a network of 
underground cables. 

In many parts of the world, especially in America, 
water power is utilized to a considerable extent instead of 
steam for the generation of electric current. The immense 
volume of water passing over the Falls of Niagara develops 
energy equal to about seven million horse-power, and a 
small amount of this energy, roughly about three-quarters 
of a million horse-power, has been harnessed and made to 
produce electric current for light and power. The water 
passes down a number of penstocks, which are tubes or 
tunnels about 7 feet in diameter, lined with brick and 
concrete; and at the bottom of these tubes are placed 
powerful water turbines. The falling water presses upon 
the vanes of the turbines, setting them revolving at great 
speed, and the power produced in this way is used to drive 
a series of very large alternating current dynamos. The 
current is conveyed at a pressure of about 60,000 volts 
to various towns within a radius of 200 or 300 miles, 
and it is anticipated that before very long the supply will 

F 8l 


Electricity 

be extended to towns still more distant. Many other 
American rivers have been harnessed in a similar way, 
though not to the same extent; and Switzerland and 
Norway are utilizing their water power on a rapidly 
increasing scale. In England, owing to the abundance of 
coal, little has been done in this direction. Scotland is 
well favoured in the matter of water power, and it is 
estimated that the total power available is considerably 
more than enough to run the whole of the railways of that 
country. Very little of this power has been utilized how¬ 
ever, and the only large hydro-electric installation is the 
one at Kinlochleven, in Argyllshire. It is a mistake to 
suppose that water power means power for nothing, but 
taking things all round the cost of water power is consider¬ 
ably lower than that of steam. 


\ 


82 


CHAPTER XI 


ELECTRICITY IN LOCOMOTION 

The electric tramcar has become such a necessary feature 
of our everyday life that it is very difficult to realize how 
short a time it has been with us. To most of us a horse- 
drawn tramcar looks like a relic of prehistoric times, and 
yet it is not so many years since the horse tram was in full 
possession of our streets. Strikes of tramway employees 
are fortunately rare events, but a few have occurred during 
the past two or three years in Leeds and in other towns, 
and they have brought home to us our great dependence 
upon the electric tram. During the Leeds strike the streets 
presented a most curious appearance, and the city seemed 
to have made a jump backward to fifty years ago. Every 
available article on wheels was pressed into service to bring 
business men into the city from the outlying districts, and 
many worthy citizens were seen trying to look dignified 
and unconcerned as they jogged along in conveyances 
which might have come out of the Ark. On such an 
occasion as this, if we imagine the electric light supply 
stopped also, we can form some little idea of our indebted¬ 
ness to those who have harnessed electricity and made it 
the greatest power of the twentieth century. 

There are three distinct electric tramway systems; the 
trolley or overhead system, the surface contact system, 
and the conduit system. The trolley system has almost 
driven the other two from the field, and it is used almost 

83 


Electricity 

exclusively throughout Great Britain and Ireland. On the 
Continent and in the United States the conduit system still 
survives, but probably it will not be long before the trolley 
system is universally employed. 

The superiority of the trolley system lies in the fact that 
it is cheaper to construct and to maintain than the other 
two, and also in its much greater reliability under all 
working conditions. The overhead wire is not one con¬ 
tinuous cable, but is divided into sections of about half a 
mile in length, each section being supplied with current 
from a separate main. At each point where the current 
is fed to the trolley wire a sort of metal box may be seen 
at the side of the street. These boxes are called “feeder 
pillars,” and each contains a switch by means of which the 
current can be cut off from that particular section, for 
repairing or other purposes. Above the car is fixed an arm 
provided with a trolley wheel which runs along the wire, ’ 
and this wheel takes the current from the wire. From the 
wheel the current passes down the trolley arm to the 
controller, which is operated by the driver, and from there 
to the motors beneath the car. Leaving the motors it 
passes to the wheels and then to the rails, from which it 
is led off at intervals by cables and so returned to the 
generating station. The current carried by the rails is at 
a pressure of only a few volts, so that there is not the 
slightest danger of shock from them. There are generally 
two electric motors beneath the car, and the horse-power 
of each varies from about fifteen to twenty-five. 

The controller consists mainly of a number of graduated 
resistances. To start the car the driver moves a handle 
forward notch by notch, thus gradually cutting out the 
resistance, and so the motors receive more and more 
current until they are running at full speed. The move¬ 
ment of the controller handle also alters the connexion of 

84 


Electricity in Locomotion 

the motors. When the car is started the motors are 
connected in series, so that the full current passes through 
each, while the pressure is divided between them; but 
when the car is well on the move the controller connects 
the motors in parallel, so that each receives the full pressure 
of the current. 

The conduit and surface contact systems are much the 
same as the trolley system except in the method of supply¬ 
ing the current to the cars. In the conduit system two 
conductors conveying the current are placed in an under¬ 
ground channel or conduit of concrete strengthened by iron 
yokes. The top of the conduit is almost closed in so as to 
leave only a narrow slot, through which passes the current 
collector of the car. This current collector, or “ plough ” as 
it is called, carries two slippers which make contact with the 
conductors, and thus take current from them. In this 
system the current returns along one of the conductors, so 
that no current passes along the track rails. This is the 
most expensive of the three systems, both in construction 
and maintenance. 

The surface contact or stud system is like the conduit 
system in having conductors placed in a sort of under¬ 
ground trough, but in this case contact with the conductors 
is made by means of metal studs fixed at intervals in the 
middle of the track. The studs are really the tops of 
underground boxes each containing a switch, which, when 
drawn up to a certain position, connects the stud to the 
conductors. These switches are arranged to be moved by 
magnets fixed beneath the car, and thus when the car 
passes over a stud the magnets work the switch and con¬ 
nect the stud to the conductors, so that the stud is then 
“alive.” The current is taken from the studs by means of 
sliding brushes or skates which are carried by the car. 
The studs are thus alive only when the car is passing over 

85 


Electricity 

them, and at all other times they are dead, and not in any 
way dangerous. 

The weight and speed of electric cars make it important 
to have a thoroughly reliable system of brakes. First of 
all there are ordinary mechanical brakes, which press 
against the wheels. Then there are electro-magnetic 
slipper brakes which press on the rails instead of on the 
wheels of the car. These brakes are operated by electro¬ 
magnets of great power, the current necessary to excite the 
magnets being taken from the motors. Finally there is 
a most interesting and ingenious method of regenerative 
control. Before a car can be stopped after it has attained 
considerable speed a certain amount of energy has to be 
got rid of in some way. With the ordinary mechanical or 
electro-magnetic brakes this energy is wasted, but in the 
regenerative method it is turned into electric current, which 
is sent back into the circuit. If an electric motor is supplied 
with mechanical power instead of electric current it becomes 
a dynamo, and generates current instead of using it. In 
the regenerative system, when a car is “coasting” down a 
hill it drives the wheels, and the wheels drive the motors, 
so that the latter become dynamos and generate current 
which is sent back to the power station. In this way some 
of the abnormal amount of current taken by a car in climbing 
a hill is returned when the car descends the hill. The 
regenerative system limits the speed of the car, so that it 
cannot possibly get beyond control. 

A large tramway system spreads outwards from the 
centre of a city to the suburbs, and usually terminates at 
various points on the outskirts of these suburbs. It often 
happens that there are villages lying some distance beyond 
these terminal points, and it is very desirable that there 
should be some means of transport between these villages 
and the city. An extension of the existing tramway is not 

86 


PLATE VII 



By permission of Siemens brothers Dynamo U'orks Ltd, 

ELECTRIC COLLIERY RAILWAY. 



























Electricity in Locomotion 

practicable in many cases, because the traffic would not be 
sufficient to pay for the heavy outlay, and also because the 
road may not be of sufficient width to admit of cars running 
on a fixed track. The difficulty may be overcome satis¬ 
factorily by the use of trackless trolley cars. With these 
cars the costly business of laying a rail track is altogether 
avoided, only a system of overhead wires being necessary. 
As there is no rail to take the return current, a second 
overhead wire is required. The car is fitted with two 
trolley arms, and the current is taken from one wire by the 
first arm, sent through the controller and the motors, and 
returned by the second arm to the other wire, and so back 
to the generating station. The trolley poles are so ar¬ 
ranged that they allow the car to be steered round obstruc¬ 
tions or slow traffic, and the car wheels are usually fitted 
with solid rubber tyres. Trackless cars are not capable of 
dealing with a large traffic, but they are specially suitable 
where an infrequent service, say a half-hourly one, is enough 
to meet requirements. 

We come now to electric railways. These may be 
divided into two classes, those with separate locomotives 
and those without. The separate locomotive method is 
largely used for haulage purposes in collieries and large 
works of various kinds. In Plate VII. is seen an electric 
locomotive hauling a train of coal waggons in a colliery 
near the Tyne, and it will be seen that the overhead 
system is used, the trolley arm and wheel being replaced 
by sliding bows. In a colliery railway it is generally 
impossible to select the most favourable track from the 
railway constructors point of view, as the line must be 
arranged to serve certain points. This often means taking 
the line sometimes through low tunnels or bridges where 
the overhead wire must be low, and sometimes over public 
roads where the wire must be high ; and the sliding bow 

87 


Electricity 

is better able than the trolley arm and wheel to adapt 
itself to these variations. In the colliery where this loco¬ 
motive is used the height of the overhead wire ranges 
from io feet 6 inches through tunnels or bridges, to 21 feet 
where the public road is crossed. The locomotive weighs 
33! tons, and has four electric motors each developing 
50 horse-power with the current employed. It will be 
noticed that the locomotive has two sets of buffers. This 
is because it has to deal with both main line waggons and 
the smaller colliery waggons, the upper set of buffers being 
for the former, and the lower and narrower set for the 
latter. Plate VIII. shows a 50-ton locomotive on the 
British Columbia Electric Railway, and a powerful locomo¬ 
tive in use in South America. In each case it will be 
seen that the trolley wheel is used. 

In this country electric railways for passenger traffic 
are mostly worked on what is known as the multiple-unit 
system, in which no separate locomotives are used, the 
motors and driving mechanism being placed on the cars 
themselves. There are also other cars without this equip¬ 
ment, so that a train consists of a single motor-car with or 
without trailer, or of two motor-cars with trailer between, 
or in fact of any other combination. When a train 
contains two or more motor-cars all the controllers, which 
are very similar to those on electric tramcars, are electric¬ 
ally connected so as to be worked together from one 
master controller. This system allows the length of the 
train to be adjusted to the number of passengers, so that 
no power is wasted in running empty cars during periods 
of small traffic. In suburban railways, where the stopping- 
places are many and close together, the efficiency of the 
service depends to a large extent upon the time occupied 
in bringing the trains from rest to full speed. In this 
respect the electric train has a great advantage over the 

88 


Electricity in Locomotion 

ordinary train hauled by a steam locomotive, for it can 
pick up speed at three or more times the rate of the latter, 
thus enabling greater average speeds and a more frequent 
service to be maintained. 

Electric trains are supplied with current from a central 
generating station, just as in the case of electric tramcars, 
but on passenger lines the overhead wire is in most cases 
replaced by a third rail. This live rail is placed upon 
insulators just outside the track rail, and the current is 
collected from it by sliding metal slippers which are carried 
by the cars. The return current may pass along the 
track rails as in the case of trolley tramcars, or be con¬ 
veyed by another insulated conducting rail running along 
the middle of the track. 

The electric railways already described are run on con¬ 
tinuous current, but there are also railways run on alternat¬ 
ing current. A section of the London, Brighton, and South 
Coast Railway is electrically operated by alternating 
current, the kind of current used being that known as 
single-phase. The overhead system is used, and the 
current is led to the wire at a pressure of about 6000 volts. 
This current is collected by sliding bows and conveyed to 
transformers carried on the trains, from which it emerges 
at a pressure of about 300 volts, and is then sent through 
the motors. The overhead wires are not fixed directly to 
the supports as in the case of overhead tramway wires, but 
instead two steel cables are carried by the supports, and 
the live wires are hung - from these. The effect of this 
arrangement is to make the sliding bows run steadily and 
evenly along the wires without jumping or jolting. If ever 
electricity takes the place of steam for long distance rail¬ 
way traffic, this system, or some modification of it, prob¬ 
ably will be employed. 

Mention must be made also of the Kearney high speed 

89 


Electricity 

electric mono-railway. In this system the cars, which are 
electrically driven, are fitted above and below with grooved 
wheels. The lower wheels run on a single central rail 
fixed to sleepers resting on the ground, and the upper 
wheels run on an overhead guide rail. It is claimed that 
speeds of 150 miles an hour are attainable with safety and 
economy in working. This system is yet only just out of 
the experimental stage, but its working appears to be 
exceedingly satisfactory. 

A self-contained electric locomotive has been con¬ 
structed by the North British Locomotive Company. It 
is fitted with a steam turbine which drives a dynamo gener¬ 
ating continuous current, and the current is used to drive 
four electric motors. This locomotive has undergone ex¬ 
tensive trials, but its practical value as compared with the 
ordinary type of electric locomotive supplied with current 
from an outside source is not yet definitely established. 

At first sight it appears as though the electric storage 
cell or accumulator ought to provide an almost perfect 
means of supplying power for self-propelled electric vehicles 
of all kinds. In practice, however, it has been found that 
against the advantages of the accumulator there are to-be 
set certain great drawbacks, which have not yet been 
overcome. Many attempts have been made to apply 
accumulator traction to electric tramway systems, but they 
have all failed, and the idea has been abandoned. There 
are many reasons for the failure of these attempts. The 
weight of a battery of accumulators large enough to run a 
car with a load of passengers is tremendous, and this is 
of course so much dead weight to be hauled along, and it 
becomes a very serious matter when steep hills have to be 
negotiated. When a car is started on a steep up-gradient 
a sudden and heavy demand for current is made, and this 
puts upon the accumulators a strain which they are not 

90 


Electricity in Locomotion 

able to bear without injury. Another great drawback is 
the comparatively short time for which accumulators can 
give a heavy current, for this necessitates the frequent 
return of the cars to the central station in order to have 
the batteries re-charged. Finally, accumulators are sensi¬ 
tive things, and the continuous heavy vibration of a tram- 
car is ruinous to them. 

The application of accumulators to automobiles is much 
more feasible, and within certain limits the electric motor¬ 
car may be considered a practical success. The electric 
automobile is superior to the petrol-driven car in its delight¬ 
fully easy and silent running, and its freedom from all 
objectionable smells. On the other hand high speeds 
cannot be attained, and there is the trouble of having the 
accumulators re-charged, but for city work this is not a 
serious matter. Two sets of accumulators are used, so that 
one can be left at the garage to be charged while the other 
is in use, the replacing of the exhausted set by the freshly 
charged one being a matter of only a few minutes. The 
petrol-driven car is undoubtedly superior in every way for 
touring purposes. Petrol can now be obtained practically 
anywhere, whereas accumulator charging stations are com¬ 
paratively few and far between, especially in country 
districts ; and there is no comparison as regards convenience 
between the filling of a petrol tank and the charging of a 
set of accumulators, for one process takes a few minutes 
and the other a few hours. 

Accumulator-driven locomotives are not in general use, 
but for certain special purposes they have proved very 
satisfactory. A large locomotive of this kind was used for 
removing excavated material and for taking in the iron 
segments, sleepers, rails, and other materials in the con¬ 
struction of the Great Northern, Piccadilly, and Brompton 
Tube Railway. This locomotive is 50 feet 6 inches long, 

9i 


Electricity 

and it carries a battery of eighty large “ chloride ” cells, the 
total weight of locomotive and battery being about 64 
tons. It is capable of hauling a load of 60 tons at a 
rate of from 7 to 9 miles an hour on the level. 

Amongst the latest developments of accumulator traction 
is a complete train to take the place of a steam locomotive 
hauling a single coach on the United Railways of Cuba. 
According to the Scientific American the train consists 
of three cars, each having a battery of 216 cells, supplying 
current at 200 volts to the motors. Each car has accommo¬ 
dation for forty-two passengers, and the three are arranged 
to work on the multiple-unit system from one master con¬ 
troller. The batteries will run from 60 to 100 miles for 
each charging of seven hours. 


92 


CHAPTER XII 


ELECTRIC LIGHTING 

In the first year of the nineteenth century one of the 
greatest of England’s scientists, Sir Humphry Davy, 
became lecturer on chemistry to the Royal Institution, 
where his brilliant lectures attracted large and enthusiastic 
audiences. He was an indefatigable experimenter, and in 
order to help on his work the Institution placed at his 
disposal a very large voltaic battery consisting of 2000 
cells. In 1802 he found that if two rods of carbon, one 
connected to each terminal of his great battery, were 
first made to touch one another and then gradually 
separated, a brilliant arch of light was formed between 
them. The intense brilliance of this electric arch, or arc 
as it came to be called, naturally suggested the possibility 
of utilizing Davy’s discovery for lighting purposes, but the 
maintaining of the necessary current proved a serious 
obstacle. The first cost of a battery of the required size 
was considerable, but this was a small matter compared 
with the expense of keeping the cells in good working 
order. Several very ingenious and more or less efficient 
arc lamps fed by battery current were produced by various 
inventors, but for the above reason they were of little use 
except for experimental purposes, and the commercial 
success of the arc lamp was an impossibility until the 
dynamo came to be a really reliable source of current. 
Since that time innumerable shapes and forms of arc lamps 

93 


Electricity 

have been devised, while the use of such lamps has in¬ 
creased by leaps and bounds. To-day, wherever artificial 
illumination on a large scale is required, there the arc lamp 
is to be found. 

When the carbon rods are brought into contact and 
then slightly separated, a spark passes between them. 
Particles of carbon are torn off by the spark and volatilized, 
and these incandescent particles form a sort of bridge which 
is a sufficiently good conductor for the current to pass 
across it from one rod to the other. When the carbons 
are placed horizontally, the glowing mass is carried upwards 
by the ascending currents of heated air, and it assumes the 
arch-like form from which it gets its name. If the carbons 
are vertical the curve is not produced, a more or less 
straight line being formed instead. The electric arc may be 
formed between any conducting substances, but for practical 
lighting purposes carbon is found to be most suitable. 

Either continuous or alternating currents may be used 
to form the arc. With continuous current, if the carbon 
rods are fully exposed to the air, they gradually consume 
away, and minute particles of carbon are carried across 
from the positive rod to the negative rod, so that the former 
wastes at about twice the rate of the latter. The end of 
the positive rod becomes hollowed out so as to resemble a 
little crater, and the end of the negative rod becomes more 
or less pointed. The fact that with continuous current the 
positive rod consumes away twice as fast as the negative 
rod, may be taken advantage of to decrease the cost of new 
carbons, by replacing the wasted positive rod with a new 
one, and using the unconsumed portion of the old positive 
rod as a new negative rod. 1 If alternating current is used, 
each rod in turn becomes the positive rod, so that no crater 

1 In actual practice the positive carbon is made double the thickness of the 
negative, so that the two consume at about the same rate. 

94 


Electric Lighting 

is formed, and both the carbons have the same shape and 
are consumed at the same rate. A humming noise is liable 
to be produced by the alternating current arc, but by care¬ 
ful construction of the lamp this noise is reduced to the 
minimum. 

If the carbons are enclosed in a suitable globe the 
rate of wasting is very much less. The oxygen inside the 
globe becomes rapidly consumed, and although the globe 
is not air-tight, the heated gases produced inside it check 
the entrance of further supplies of fresh air as long as the 
lamp is kept burning. When the light is extinguished, 
and the lamp cools down, fresh air enters again freely. 

Arc lamp carbons may be either solid or cored. The 
solid form is made entirely of very hard carbon, while the 
cored form consists of a narrow tube of carbon filled up with 
soft graphite. Cored carbons usually burn more steadily 
than the solid form. In what are known as flame arc 
lamps the carbons are impregnated with certain metallic 
salts, such as calcium. These lamps give more light for 
the same amount of current. The arc is long and flame¬ 
like, and usually of a striking yellow colour, but it is not so 
steady as the ordinary arc. 

As the carbon rods waste away, the length of the arc 
increases, and if this increase goes beyond a certain limit 
the arc breaks and the current ceases. If the arc is to be 
kept going for any length of time some arrangement for 
pushing the rods closer together must be provided, in order 
to counteract the waste. In arc lamps this pushing to¬ 
gether, or “feeding” as it is called, is done automatically, as 
is also the first bringing together and separating of the rods 
to start or strike the arc. Fig. 21 shows a simple arrange¬ 
ment for this purpose. A is the positive carbon, and B 
the negative. C is the holder for the positive carbon, and 
this is connected to the rod D, which is made of soft iron. 

95 


Electricity 

This rod is wound with two separate coils of wire as shown, 
coil E having a low resistance, and coil F a high one. 
These two coils are solenoids, and D is the core, 
(Chapter VII.). When the lamp is not in use, the weight of 
the holder keeps the positive carbon in contact with the 
negative carbon. When switched on, the current flows 
along the cable to the point H. Here it has two paths 
open to it, one through coil E to the positive carbon, and 
the other through coil F and back to the source of supply. 

But coil E has a much lower 
resistance than coil F, and 
so most of the current 
chooses the easier path 
through E, only a small 
amount of current taking 
the path through the other 
coil. Both coils are now 
magnetized, and E tends to 
draw the rod D upwards, 
while F tends to pull it 
downwards. Coil E, how¬ 
ever, has much greaterpower 
than coil F, because a much 
larger amount of current is 
passing through it; and so it overcomes the feeble pull of F, 
and draws up the rod. The raising of D lifts the positive 
carbon away from the negative carbon, and the arc is struck. 
The carbons now begin to waste away, and very slowly the 
distance between them increases. The path of the current 
passing through coil E is from carbon A to carbon B by 
way of the arc, and as the length of the gap between A 
and B increases, the resistance of this path also increases. 
The way through coil E thus becomes less easy, and as 
time goes on more and more current takes the alternative 

96 



Fig. 21.—Diagram showing simple 
method of carbon regulation for 
Arc Lamps. 




















PLATE IX. 




NIGHT PHOTOGRAPHS, TAKEN BY THE LIGHT OF THE ARC LAMPS. 





















Electric Lighting 

path through coil F. This results in a decrease in the 
magnetism of E, and an increase in that of F, and at a 
certain point F becomes the more powerful of the two, and 
pulls down the rod. In this way the positive carbon is 
lowered and brought nearer to the negative carbon. 
Directly the diminishing distance between A and B reaches 
a certain limit, coil E once more asserts its superiority, and 
by overcoming the pull of F it stops the further approach 
of the carbons. So, by the opposing forces of the two 
coils, the carbons are maintained between safe limits, in 
spite of their wasting away. 

The arc lamp is largely used for the illumination 
of wide streets, public squares, railway stations, and the 
exteriors of theatres, music-halls, picture houses, and large 
shops. The intense brilliancy of the light produced may be 
judged from the accompanying photographs (Plate IX.), 
which were taken entirely by the light of the arc lamps. 
Still more powerful arc lamps are constructed for use in 
lighthouses. The illuminating power of some of these 
lamps is equal to that of hundreds of thousands of 
candles, and the light, concentrated by large reflectors, is 
visible at distances varying from thirty to one hundred 
miles. 

Arc lamps are also largely used for lighting interiors, 
such as large showrooms, factories or workshops. For 
this kind of lighting the dazzling glare of the outdoor 
lamp would be very objectionable and harmful to the eyes, 
so methods of indirect lighting are employed to give a soft 
and pleasant light. Most of the light in the arc lamp comes 
from the positive carbon, and for ordinary outdoor lighting 
this carbon is placed above the negative carbon. In lamps 
for interior lighting the arrangement is frequently reversed, 
so that the positive carbon is below. Most of the light is 
thus directed upwards, and if the ceiling is fairly low and 
G 97 


Electricity 

of a white colour the rays are reflected by it, and a soft and 
evenly diffused lighting is the result. Some light comes 
also from the negative carbon, and those downward rays 
are reflected to the ceiling by a reflector placed beneath the 
lamp. Where the ceiling is very high or of an unsuitable 
colour, a sort of artificial ceiling in the shape of a large 
white reflector is placed above the lamp to produce the 
same effect. Sometimes the lamp is arranged so that part 
of the light is reflected to the ceiling, and part transmitted 
directly through a semi-transparent reflector below the 
* lamp. The composition of the light of the arc lamp is very 
similar to that of sunlight, and by the use of such lamps the 
well-known difficulty of judging and matching colours by 
artificial light is greatly reduced. This fact is of great 
value in drapery establishments, and the arc lamp has 
proved a great success for lighting rooms used for night 
painting classes. 

The powerful searchlights used by warships are arc 
lamps provided with special arrangements for projecting 
the light in any direction. A reflector behind the arc con¬ 
centrates the light and sends it out as a bundle of parallel 
rays, and the illuminating power is such that a good search¬ 
light has a working range of nearly two miles in clear 
weather. According to the size of the projector, the 
illumination varies from about 3000 to 30,000 or 40,000 
candle-power. For some purposes, such as the illuminating 
of narrow stretches of water, a wider beam is required, and 
this is obtained by a diverging lens placed in front of the 
arc. In passing through this lens the light is dispersed or 
spread out to a greater or less extent according to the 
nature of the lens. Searchlights are used in navigating 
the Suez Canal by night, for lighting up the buoys along 
the sides of the canal. The ordinary form of searchlight 
does this quite well, but at the same time it illuminates 

98 


Electric Lighting 

equally an approaching vessel, so that the pilot on this 
vessel is dazzled by the blinding glare. To avoid this 
dangerous state of things a split reflector is used, which 
produces two separate beams with a dark space between 
them. In this way the sides of the canal are illuminated, 
but the light is not thrown upon oncoming vessels, so that 
the pilots can see clearly. 

Glass reflectors are much more efficient than metallic 
ones, but they have the disadvantage of being easily put 
out of action by gunfire. This defect is remedied by pro¬ 
tecting the glass reflector by a screen of wire netting. 
This is secured at the back of the reflector, and even if the 
glass is shattered to a considerable extent, as by a rifle 
bullet, the netting holds it together, and keeps it quite 
serviceable. Reflectors protected in this way are not put 
out of action by even two or three shots fired through 
them. Searchlight arcs and reflectors are enclosed in metal 
cylinders, which can be moved in any direction, vertically 
or horizontally. 

In the arc lamps already described, a large proportion 
of the light comes from the incandescent carbon electrodes. 
About the year 1901 an American electrician, Mr. P. C. 
Hewitt, brought out an arc lamp in which the electrodes 
took no part in producing the light, the whole of which 
came from a glowing stream of mercury vapour. This 
lamp, under the name of the Cooper-Hewitt mercury 
vapour lamp, has certain advantages over other electric 
illuminants, and it has come into extensive use. 

It consists of a long glass tube, exhausted of air, and 
containing a small quantity of mercury. Platinum wires to 
take the current from the source of supply are sealed in at 
each end. The tube is attached to a light tubular frame¬ 
work of metal suspended from the ceiling, and this frame 
is arranged so that it can be tilted slightly downwards by 

99 


Electricity 

pulling a chain. As shown in Fig. 22, the normal position 
of the lamp is not quite horizontal, but tilted slightly down¬ 
wards towards the end of the tube having the bulb con¬ 
taining the mercury. The platinum wire at this end dips 
into the mercury, so making a metallic contact with it. 
The lamp is lighted by ( switching on the current and pulling 
down the chain. The altered angle makes the mercury 
flow along the tube towards the other platinum electrode, 
and as soon as it touches this a conducting path for the 


Ceiling 



£ 

Fig. 22.—Sketch of Mercury Vapour Lamp. 


current is formed from end to end of the tube. The lamp 
is now allowed to fall back to its original angle, so that the 
mercury returns to its bulb. There is now no metallic con¬ 
nexion between the electrodes, but the current continues 
to pass through the tube as a vacuum discharge. Some 
of the mercury is immediately vaporized and rendered 
brilliantly incandescent, and so the light is produced. The 
trouble of pulling down the chain is avoided in the 
automatic mercury vapour lamp, which is tilted by an 
electro-magnet. This magnet is automatically cut out of 

100 






Electric Lighting 

circuit as soon as the tilting is completed and the arc 
struck. 

The average length of the tube in the ordinary form of 
mercury vapour lamp is about 30 inches, and a light of 
from 500 to 3000 candle-power is produced, according to 
the current used. Another form, known as the “Silica” 
lamp, is enclosed in a globe like that of an ordinary electric 
arc lamp. The tube is only about 5 or 6 inches in 
length, and it is made of quartz instead of glass, the 
arrangements for automatically tilting the tube being 
similar to those in the ordinary form of lamp. 

The light of the mercury vapour lamp is different from 
that of all other lamps. Its peculiarity is that it contains 
practically no red rays, most of the light being yellow, with 
a certain proportion of green and blue. The result is a 
light of a peacock-blue colour. The absence of red rays 
alters colour-values greatly, scarlet objects appearing 
black ; and on this account it is impossible to match colours 
by this light. In many respects, however, the deficiency 
in red rays is a great positive advantage. Every one who 
has worked by mercury vapour light must have noticed 
that it enables very fine details to be seen with remarkable 
distinctness. This property is due to an interesting fact. 
Daylight and ordinary artificial light is a compound or 
mixture of rays of different colours. It is a well-known 
optical fact that a simple lens is unable to bring all these 
rays to the same focus ; so that if we sharply focus an image 
by red light, it is out of focus or blurred by blue light. This 
defect of the lens is called “chromatic aberration.” The 
eye too suffers from chromatic aberration, so that it cannot 
focus sharply all the different rays at the same time. The 
violet rays are brought to a focus considerably in front of 
the red rays, and the green and the yellow rays come in 
between the two. The eye therefore automatically and 

101 


Electricity 

unconsciously effects a compromise, and focuses for the 
greenish-yellow rays. The mercury vapour light consists 
very largely of these rays, and consequently it enables the 
image to be focused with greater sharpness ; or, in other 
words, it increases the acuteness of vision. Experiments 
carried out by Dr. Louis Bell and Dr. C. H. Williams 
demonstrated this increase in visual sharpness very con¬ 
clusively. Type, all of exactly the same size, was examined 
by mercury vapour light, and by the light from an electric 
incandescent lamp with tungsten filament. The feeling of 
sharper definition produced by the mercury vapour light 
was so strong that many observers were certain that the 
type was larger, and they were convinced that it was 
exactly the same only after careful personal examination. 

Mercury vapour light apparently imposes less strain 
upon the eyes than ordinary artificial light, and this 
desirable feature is the result of the absence of the red rays, 
which, besides having little effect in producing vision, are 
tiring to the eyes on account of their heating action. The 
light is very highly actinic, and for this reason it is largely 
used for studio and other interior photographic work. In 
cases where true daylight colour effects are necessary, a 
special fluorescent reflector is used with the lamp. By 
transforming the frequency of the light waves, this reflector 
supplies the missing red and orange rays, the result being 
a light giving normal colour effects. 

Another interesting vapour lamp may be mentioned 
briefly. This has a highly exhausted glass tube containing 
neon, a rare gas discovered by Sir William Ramsay. The 
light of this lamp contains no blue rays, and it is of a 
striking red colour. Neon lamps are used chiefly for 
advertising purposes, and they are most effective for 
illuminated designs and announcements, the peculiar and 
distinctive colour of the light attracting the eye at once. 

102 


Electric Lighting 

An electric current meets with some resistance in 
passing through any substance, and if the substance is a 
bad conductor the resistance is very great. As the current 
forces its way through the resistance, heat is produced, and 
a very thin wire, which offers a high resistance, may be 
raised to a white heat by an electric current, and it then 
glows with a brilliant light. This fact forms the basis of 
the electric incandescent or glow lamp. 

In the year 1878, Thomas A. Edison set himself the 
task of producing a perfect electric incandescent lamp, 
which should be capable of superseding gas for household 
and other interior lighting. The first and the greatest 
difficulty was that of finding a substance which could be 
formed into a fine filament, and which could be kept 
in a state of incandescence without melting or burning 
away. Platinum was first chosen, on account of its very 
high melting-point, and the fact that it was not acted 
upon by the gases of the air. Edison’s earliest lamps 
consisted of a piece of very thin platinum wire in the 
shape of a spiral, and enclosed in a glass bulb from which 
the air was exhausted. The ends of the spiral were 
connected to outside wires sealed into the bulb. It was 
found, however, that keeping platinum continuously at a 
high temperature caused it to disintegrate slowly, so that 
the lamps had only a short life. Fine threads or filaments 
of carbon were then tried, and found to be much more 
durable, besides being a great deal cheaper. The carbon 
filament lamp quickly became a commercial success, and 
up to quite recent years it was the only form of electric 
incandescent lamp in general use. 

In 1903 a German scientist, Dr. Auer von Welsbach, 
of incandescent gas mantle fame, produced an electric lamp 
in which the filament was made of the metal osmium, and 
this was followed by a lamp using the metal tantalum for 

103 


Electricity 

the filament, the invention of Siemens and Halske. For a 
while the tantalum lamp was very successful, but more 
recently it has been superseded in popularity by lamps 
having a filament of the metal tungsten. The success of 
these lamps has caused the carbon lamp to decline in 
favour. The metal filaments become incandescent much 
more easily than the carbon filament, and for the same 
candle-power the metal filament lamp consumes much less 
current than the carbon lamp. 

The construction of tungsten lamps is very interesting. 
Tungsten is a very brittle metal, and at first the lamps 
were fitted with a number of separate filaments. These 
were made by mixing tungsten powder with a sort of paste, 
and then squirting the mixture through very small 
apertures, so that it formed hair-like threads. Early in 
1911 lamps having a filament consisting of a single con¬ 
tinuous piece of drawn tungsten wire were produced. It 
had been known for some time that although tungsten was 
so brittle at ordinary temperatures, it became quite soft 
and flexible when heated to incandescence in the lamp, and 
that it lost this quality again as soon as it cooled down. 
A process was discovered by which the metal could be 
made permanently ductile, by mechanical treatment while 
in the heated state. In this process pure tungsten powder 
is pressed into rods and then made coherent by heating. 
While still hot it is hammered, and finally drawn out into 
fine wires through diamond dies. The wire is no thicker 
than a fine hair, and it varies in size from about o'Oi2 mm. 
to about 0*375 mm., according to the amount of current it 
is intended to take. It is mounted by winding it con¬ 
tinuously zigzag shape round a glass carrier, which has at 
the top and the bottom a number of metal supports 
arranged in the form of a star, and insulated by a central 
rod of glass. One star is made of strong, stiff material, 

104 


Electric Lighting 

and the other consists of fine wires of some refractory 
metal, molybdenum being used in the Osram lamps. 
These supports act as springs, and keep the wire securely 
in its original shape, no matter in what position the lamp 
is used. The whole is placed in a glass bulb, which is 
exhausted of air and sealed up. 

For some purposes lamps with specially small bulbs are 
required, and in these the tungsten wire is made in the 
shape of fine spirals, instead of in straight pieces, so that 
it takes up much less room. In the “Axial” lamp the 
spiral is mounted in such a position that most of the light 
is sent out in one particular direction. 

The latest development in electric incandescent lamps is 
the “ half-watt ” lamp. The watt is the standard of electrical 
energy, and it is the rate of work represented by a current 
of one ampere at a pressure of i volt. With continuous 
currents the watts are found very simply by multiplying 
together the volts and the amperes. For instance, a 
dynamo giving a current of 20 amperes at a pressure 
of 50 volts would be called a 1000-watt dynamo. 
With alternating currents the calculation is more compli¬ 
cated, but the final result is the same. The ordinary form 
of tungsten lamp gives about one candle-power for every 
watt, and is known as a one-watt lamp. As its name 
suggests, the half-watt lamp requires only half this amount 
of energy to give the same candle-power, so that it is very 
much more economical in current. In this lamp the 
tungsten filament is wound in a spiral, but instead of being 
placed in the usual exhausted bulb, it is sealed into a bulb 
containing nitrogen gas. The increased efficiency is 
obtained by running the filament at a temperature from 
400° to 6oo° C. higher than that at which the filament in 
the ordinary lamp is used. 

In spite of the great advances in artificial lighting 

105 


Electricity 

made during recent years, no one has yet succeeded in 
producing light without heat. This heat is not wanted, 
and it represents so much waste energy. It has often been 
said that the glow-worm is the most expert of all illumina¬ 
ting engineers, for it has the power of producing at will a 
light which is absolutely without heat. Perhaps the nearest 
approach to light without heat is the so-called “cold light” 
invented by M. Dussaud, a French scientist. His device 
consists of a revolving ring of exactly similar tungsten 
lamps. Each of these lamps has current passed through it 
in turn, and the duration of the current in each is so short, 
being only a fraction of a second, that the lamp has not 
sufficient time to develop any appreciable amount of heat. 
The light from the ring of lamps is brought to a focus, and 
passed through a lens to wherever it is required. Electric 
incandescent lamps are made in a variety of sizes, each one 
being intended for a certain definite voltage. If a lamp 
designed for, say, 8 volts, is used on a circuit of 
32 volts, its candle-power is greatly increased, while the 
amount of current consumed is not increased in proportion. 
In this way the lamp becomes a more efficient source 
of light, but the “over-running,” as it is called, has a 
destructive effect on the filament, so that the life of the 
lamp is greatly shortened. In the Dussaud system how¬ 
ever the time during which each lamp has current passing 
through it is so short, followed by a period of rest, that 
the destructive effect of over-running is reduced to the 
minimum ; so that by using very high voltages an ex¬ 
tremely brilliant light is safely obtained with a compara¬ 
tively small consumption of current. It might be thought 
that the constant interchange of lamps would result in an 
unsteady effect, but the substitution of one lamp for another 
is carried out so rapidly that the eye gets the impression of 
perfect steadiness. The Dussaud system is of little use 

106 


Electric Lighting 

for ordinary lighting purposes, but for lighthouse illumina¬ 
tion, photographic studio work, and the projection of 
lantern slides and cinematograph films, it appears to be of 
considerable value. 

Electric light has many advantages over all other 
illuminants. It gives off very little heat, and does not use 
up the oxygen in the air of a room as gas does; while by 
means of flexible wires the lamps can be put practically 
anywhere, so that the light may be had just where it is 
wanted. Another great advantage is that the light may be 
switched on without any trouble about matches, and there 
is none of the danger from fire which always exists with 
a flame. 

The current for electric lamps is generally taken from 
the public mains, but in isolated country houses a dynamo 
has to be installed on the premises. This is usually driven 
by a small engine running on petrol or paraffin. In order 
to avoid having to run the engine and dynamo continually, 
the current is not taken directly from the dynamo, but from 
a battery of accumulators. During the day the dynamo is 
used to charge the accumulators, and these supply the 
current at night without requiring any attention. 

Electric lighting from primary cells is out of the 
question if a good light is wanted continuously for long 
periods, for the process is far too costly and troublesome. 
If a light of small candle-power is required for periods of 
from a few minutes to about an hour, with fairly long 
intervals of rest, primary cells may be made a success. 
Large dry cells are useful for this purpose, but probably 
the most satisfactory cell is the sack Leclanch^. This is 
similar in working to the ordinary Leclanchd cell used for 
bells, but the carbon mixture is placed in a canvas bag or 
sack, instead of in a porous pot, and the zinc rod is replaced 
by a sheet of zinc surrounding the sack. These cells give 

107 


Electricity 

about i£ volt each, so that four, connected in series, 
are required to light a 6-volt lamp. The lamps must 
take only a very small current, or the cells will fail 
quickly. Small metal filament lamps taking from a third 
to half an ampere are made specially for this purpose, and 
these always should be used. A battery of sack Leclanche 
cells with a miniature lamp of this kind forms a convenient 
outfit for use as a night-light, or for lighting a dark cup¬ 
board, passage or staircase. Lamps with ruby glass, or 
with a ruby cap to slip over the bulb, may be obtained for 
photographic purposes. If the outfit is wanted for use as 
a reading-lamp it is better to have two separate batteries, 
and to use them alternately for short periods. With this 
arrangement each battery has a short spell of work followed 
by a rest, and the light may be kept on for longer periods 
without overworking the cells. 


108 


CHAPTER XIII 


ELECTRIC HEATING 

The light of the electric incandescent lamp is produced by 
the heating to incandescence of a thin filament of metal or 
carbon, and the heat itself is produced by the electric 
current forcing its way through the great resistance opposed 
to it by the filament. In such lamps the amount of heat 
produced is too small to be of much practical use, but by 
applying the same principle on a larger scale we get an 
effective electric heater. 

The most familiar and the most attractive of all electric 
heaters is the luminous radiator. This consists of two or 
more large incandescent lamps, having filaments of carbon. 
The lamps are made in the form of long cylinders, the 
glass being frosted, and they are set, generally in a vertical 
position, in an ornamental case or frame of metal. This 
case is open at the front, and has a metal reflector behind. 
The carbon filaments are raised to an orange-red heat by 
the passage of the current, and they then radiate heat rays 
which warm the bulbs and any other objects in their path. 
The air in contact with these heated bodies is warmed, 
and gradually fills the room. This form of heater, with 
its bright glowing lamps, gives a room a very cheerful 
appearance. 

In the non-luminous heaters, or “ convectors ” as they are 
called, the heating elements consist of strips of metal or 
wires having a very high resistance. These are placed in 

109 


Electricity 

a frame and made red-hot by the current. Cold air enters 
at the bottom of the frame, becomes warm by passing over 
the heating elements, and rises out at top and into the 
room. More cold air enters the frame and is heated in 
the same way, and in a very short time the whole of the 
air of the room becomes warmed. The full power of the 
heater is used in the preliminary warming of the room, but 
afterwards the temperature may be kept up with a much 
smaller consumption of current, and special regulating 
switches are provided to give different degrees of heat. 
Although these heaters are more powerful than the 
luminous radiators, they are not cheerful looking; but in 
some forms the appearance is improved by an incandescent 
lamp with a ruby glass bulb, which shines through the 
perforated front of the frame. 

The Bastian, or red glow heater, has thin wires wound 
in a spiral and enclosed in tubes made of quartz. These 
tubes are transparent both to light and heat, and so the 
pleasant glow of the red-hot wire is visible. A different 
type of heater, the hot oil radiator, is very suitable for 
large rooms. This has a wire of high resistance immersed 
in oil, which becomes hot and maintains a steady 
temperature. 

Electric cooking appliances, like the heaters just de¬ 
scribed, depend upon the heating of resistance wires or 
strips of metal. The familiar electric kettle has a double 
bottom, and in the cavity thus formed is placed the re¬ 
sistance material, protected by strips of mica, a mineral 
substance very largely used in electrical appliances of all 
kinds on account of its splendid insulating qualities. 
Electric irons are constructed in much the same way as 
kettles, and sometimes they are used with stands which 
cut off the current automatically when the iron is laid down 
upon them, so that waste and overheating are prevented. 

no 


Electric Heating 

There are also a great many varieties of electric ovens, 
grillers, hot-plates, water-heaters, glue-pots, and foot and 
bed warmers. These of course differ greatly in con¬ 
struction, but as they all work on the same principle there 
is no need to describe them. 

Electric hot-plates are used in an interesting way in 
Glasgow, to enable the police on night duty to have a hot 
supper. The plates are fitted to street telephone signal 
boxes situated at points where a number of beats join. By 
switching on current from the 
public mains the policemen 
are able to warm their food 
and tea, and a supper interval 
of twenty minutes is allowed. 

Even policemen are some¬ 
times absent-minded, and to 
avoid the waste of current and 
overheating of the plate that 
would result if a “ bobby ” 
forgot to switch off, an ar¬ 
rangement is provided which 
automatically switches off the 
current when the plate is not 
in use. 

We must turn now to 
electric heating on a much larger scale, in the electric 
furnaces used for industrial purposes. The dazzling 
brilliance of the light from the electric arc lamp is due 
to the intense heat of the stream of vaporized carbon 
particles between the carbon rods, the temperature of this 
stream being roughly about 5400° F. This great heat 
is made use of in various industries in the electric arc 
furnace. Fig. 23 is a diagram of a simple furnace of this 
kind. A is a vertical carbon rod which can be raised or 



Fig. 23.—Diagram to illustrate prin¬ 
ciple of Electric Furnace. 


Ill 









































Electricity 

lowered, and B is a bed of carbon, forming the bottom of 
the furnace, and acting as a second rod. A is lowered 
until it touches B, the current, either continuous or alter¬ 
nating, is switched on, and A is then raised. The arc is 
thus struck between A and B, and the material contained 
in the furnace is subjected to intense heat. When the 
proper stage is reached the contents of the furnace are 
drawn off at C, and fresh material is fed in from above, 
so that if desired the process may be kept going continu¬ 
ously. Besides the electric arc furnace there are also 
resistance furnaces, in which the heat is produced by 
the resistance of a conductor to a current passing 
through it. This conductor may be the actual substance 
to be heated, or some other resisting material placed close 
to it. 

It will be of interest to mention now one or two of 
the uses of electric furnaces. The well-known substance 
calcium carbide, so much used for producing acetylene gas 
for lighting purposes, is a compound of calcium and 
carbon ; it is made by raising a mixture of lime and coke 
to an intense heat in an electric furnace. The manufacture 
of calcium carbide is carried on on a very large scale at 
Niagara, with electric power obtained from the Falls, and 
at Odda in Norway, where the power is supplied by the 
river Tysse. Carborundum, a substance almost as hard 
as the diamond, is largely used for grinding and polishing 
purposes. It is manufactured by sending a strong current 
through a furnace containing a core of coke surrounded by 
a mixture of sand, sawdust, and carbon. The core be¬ 
comes incandescent, and the heating is continued until the 
carbon combines with the sand, the process taking about 
a day. Graphite, a kind of carbon, occurs naturally in the 
form of plumbago, which is used for making black lead 
pencils. It is obtained by mining, but many of the mines 

112 


Electric Heating 

are already worked out, and others will be exhausted 
before long. By means of the electric furnace, graphite 
can now be made artificially, by heating anthracite 
coal, and at Niagara a quantity running into thousands 
of tons is produced every year. Electric furnaces are 
now largely employed, particularly in France, in the 
production of the various alloys of iron which are used 
in making special kinds of steel; and they are used also 
to a considerable extent in the manufacture of quartz 
glass. 

For many years past a great deal of time and money 
has been spent in the attempt to make artificial diamonds. 
Quite apart from its use in articles of jewellery, the 
diamond has many very important industrial applications, 
its value lying in its extreme hardness, which is not 
equalled by any other substance. The very high price 
of diamonds however is at present a serious obstacle to 
their general use. If they could be made artificially on a 
commercial scale they would become much cheaper, and 
this would be of the greatest importance to many industries, 
in which various more or less unsatisfactory substitutes are 
now used on account of their much smaller cost. Recent 
experiments seem to show that electricity will solve the 
problem of diamond making. Small diamonds, one-tenth 
of an inch long, have been made in Paris by means of the 
electric arc furnace. The furnace contains calcium carbide, 
surrounded by a mixture of carbon and lime, and the arc, 
maintained by a very powerful current, is kept in operation 
for several hours. A black substance, something like coke, 
is formed round the negative carbon, and in this are found 
tiny diamonds. The diamonds continue to increase slowly 
in size during the time that the arc is at work, and it is esti¬ 
mated that they grow at the rate of about one-hundredth 
of an inch per hour. So far only small diamonds have 
h ii 3 


Electricity 

been made, but there seems to be no reason why large ones 
should not be produced, by continuing the process for three 
or four days. 

A chapter on electric heating would not be complete 
without some mention of electric welding. Welding is the 
process of uniting two pieces of metal by means of a com¬ 
bination of heat and pressure, so that a strong and perma¬ 
nent joint is produced. The chief difficulty in welding is 
that of securing and keeping up the proper temperature, 
and some metals are much more troublesome than others 
in this respect. Platinum, iron, and steel are fairly easy to 
weld, but most of the other metals, and alloys of different 
metals, require very exact regulation of temperature. It 
is almost impossible to obtain this exact regulation by 
ordinary methods of heating, but the electric current makes 
it a comparatively easy matter. The principle of ordinary 
electric welding is very simple. The ends of the two 
pieces of metal are placed together, and a powerful current 
is passed through them. This current meets with a high 
resistance at the point of contact of the two pieces, and so 
heat is produced. When the proper welding temperature 
is reached, and the metal is in a sort of pasty condition, 
the two pieces are pressed strongly together, and the 
current is switched off. The pieces are now firmly united 
together. The process may be carried out by hand, the 
welding smith switching the current on and off, and apply¬ 
ing pressure at the right moment by means of hydraulic 
power. There are also automatic welders, which perform 
the same operations without requiring any manual control. 
Alternating current is used, of low voltage but very high 
amperage. 

Steel castings are sometimes found to have small 
defects, such as cracks or blow-holes. These are not 
discarded as useless, but are made quite sound by welding 

114 


Electric Heating 

additional metal into the defective places by means of the 
electric arc. The arc is formed between the casting and a 
carbon rod, and the tremendous heat reduces the surface of 
the metal to a molten condition. Small pieces or rods of 
metal are then welded in where required. 


US 


CHAPTER XIV 


ELECTRIC BELLS AND ALARMS 

The most familiar of all electrically worked appliances is 
probably the electric bell, which in some form or other is 
in use practically all over the world. Electric bells are 
operated by means of a current of electricity sent through 
the coils of an electro-magnet, and one of the very simplest 
forms is that known as the single-stroke bell. In this bell 
an armature or piece of soft iron is placed across, but at a 
little distance from, the poles of an electro-magnet, and to 
this piece of iron is fixed a lever terminating in a sort of 
knob which lies close to a bell or gong. When a current 
is sent round the electro-magnet the armature is attracted, 
so that the lever moves forward and strikes a sharp blow 
upon the gong. Before the gong can be sounded a second 
time the current must be interrupted in order to make the 
magnet release the armature, so that the lever may fall 
back to its original position. Thus the bell gives only one 
ring each time the circuit is closed. Bells of this kind may 
be used for signalling in exactly the same way as the Morse 
sounder, and sometimes they are made with two gongs of 
different tones, which are arranged so as to be sounded 
alternately. 

For most purposes however another form called the 
trembler bell is much more convenient. Fig. 24 is a rough 
diagram of the usual arrangement of the essential parts of 
a trembler bell. When the circuit is closed by pressing the 

116 


Electric Bells and Alarms 

bell-push, a current flows from the battery to the electro¬ 
magnet EE, by way of terminal T. The electro-magnet 
then attracts the soft iron armature 
A, thus causing the hammer H to 
strike the gong. But immediately 
the armature is pulled away from 
the terminal T 1 the circuit is 
broken and the magnet loses its 
attraction for the armature, which 
is moved back again into contact 
with T 1 by the spring S. The 
circuit is thus again closed, the 
armature is again attracted, and 
the hammer strikes the gong a 
second time. This process goes 
on over and over again at a great 
speed as long as the bell-push is 
kept pressed down, resulting in 
an extremely rapid succession of 
strokes upon the gong. It will 
be noticed that the working of 
this bell is very similar to that of the automatic contact- 
breaker used for induction coils (Chapter VIII.). For 

household purposes this 
✓ - L i z zr a form of bell has completely 

driven out the once popu¬ 
lar wire-pulled bell. Bell- 
pushes are made in a 
number of shapes and 
forms, and Fig. 25 will 
make clear the working 
principle of the familiar form which greets us from almost 
every doorway with the invitation, “Press.” In private 
offices and elsewhere the rather aggressive sound of an 

117 



Fig. 24.—Mechanism of 
Electric Bell. 



Fig. 25.—Diagram showing principle 
of Bell-push. 

































Electricity 

ordinary trembler bell is apt to become a nuisance, and 
in such cases a modified form which gives a quiet buzzing 
sound is often employed. 

It is frequently necessary to have an electric bell which, 
when once started, will continue ringing until it is stopped. 
Such bells are used for fire and burglar alarms and for 
many other similar purposes, and they are called con¬ 
tinuous-ringing bells as distinguished from the ordinary 
trembler bells. In one common form of continuous-ringing 
bell two separate batteries are used, one to start the bell 
and the other to keep it ringing. When a momentary 
current from the first battery is sent over the bell lines the 
armature is attracted by the electro-magnet, and its move¬ 
ment allows a lever to fall upon a metal contact piece. 
This closes the circuit of the second battery, which keeps 
the bell ringing until the lever is replaced by pulling a cord 
or pressing a knob. Continuous-ringing bells are often 
fitted to alarm clocks. The alarm is set in the usual way, 
and at the appointed hour the bell begins to ring, and goes 
on ringing until its owner, able to stand the noise no longer, 
gets out of bed to stop it. 

There is another form of electric bell which has been 
devised to do away with the annoyance of bells suddenly 
ceasing to work on account of the failure of the battery. 
In this form the battery is entirely dispensed with, and 
the current for ringing the bell is taken from a very small 
dynamo fitted with a permanent steel horse-shoe magnet. 
The armature is connected to a little handle, and current 
is generated by twisting the handle rapidly to and fro 
between the thumb and finger. A special form of bell is 
required for this arrangement, which is not in general use. 

In the days of wire-pulled bells it was necessary to have 
quite a battery of bells of different tones for different rooms, 
but a single electric bell can be rung from bell-pushes 

118 


Electric Bells and Alarms 

placed in any part of a house or hotel. An indicator is 
used to show which push has been pressed, and, this like 
the bell itself, depends upon the attraction of an armature 
by an electro-magnet. Before reaching the bell the wire 
from each bell-push passes round a separate small electro¬ 
magnet, which is thus magnetized by the current at the 
same time that the bell is rung. In the simplest form of 
indicator the attraction of the magnet causes a little flag to 
swing backwards and forwards over its number. Another 
form is the drop indicator, in which the movement of the 
armature when attracted by the magnet allows a little flag 
to drop, thus exposing the number of the room from which 
the bell was rung. The dropped flag has to be replaced, 
either by means of a knob fixed to a rod which pushes the 
flag up again, or by pressing a push which sends the 
current through another little electro-magnet so arranged 
as to re-set the flag. 

The electric current is used to operate an almost endless 
variety of automatic alarms for special purposes. Houses 
may be thoroughly protected from undesired nocturnal 
visitors by means of a carefully arranged system of burglar 
alarms. Doors and windows are fitted with spring contacts 
so that the slightest opening of them closes a battery circuit 
and causes an alarm to sound, and even if the burglar 
succeeds in getting inside without moving a door or 
window, say by cutting out a pane of glass, his troubles are 
not by any means at an end. Other contacts are concealed 
under the doormats, and under the carpets in passages and 
stairways, so that the burglar is practically certain to tread 
on one or other of them and so rouse the house. A window 
may be further guarded by a blind contact. The blind is 
left down, and is secured at the bottom to a hook, and the 
slightest pressure upon it, such as would be given by a 
burglar trying to get through the window, sets off the alarm. 

119 


Electricity 

Safes also may be protected in similar ways, and a camera 
and flashlight apparatus may be provided, so that when the 
burglar closes the circuit by tampering with the safe he 
takes his own photograph. 

The modern professional burglar is a bit of a scientist 
in his way, and he is wily enough to find and cut the wires 
leading to the contacts, so that he can open a door or 
window at his leisure without setting off the alarm. In 
order to circumvent this little game, burglar alarms are 
often arranged on the closed-circuit principle, so that the 
alarm is sounded by the breaking of the circuit. A burglar 
who deftly cut the wires of an alarm worked on this 
principle would not be particularly pleased with the results 
of his handiwork. The bells of burglar alarms may be 
arranged to ring in a bedroom or in the street, and in the 
United States, where burglar and in fact all electric 
alarms are in more general use than in England, large 
houses are sometimes connected to a police station, so that 
the alarm is given there by bell or otherwise. 

When an outbreak of fire is discovered it is of the 
utmost importance that the nearest fire-station should be 
notified instantly, for fire spreads with such rapidity that a 
delay of even a few minutes in getting the fire-engines to 
the spot may result in the total destruction of a building 
which otherwise might have been saved. In almost all 
large towns some system of public fire alarms is now in 
use. The signal boxes are placed in conspicuous positions 
in the streets, and sometimes also in very large buildings. 
The alarm is generally given by the starting of a clockwork 
mechanism which automatically makes and breaks a circuit 
a certain number of times. When this occurs an alarm 
bell rings at the fire-station, and the number of strokes on 
the bell, which depends upon the number of times the 
alarm mechanism makes and breaks the circuit, tells the 

120 


plate X 












Electric Bells and Alarms 

attendant from which box the alarm has been given. One 
well-known form of call box has a glass front, and the 
breaking of the glass automatically closes the circuit. In 
other forms turning a handle or pulling a knob serves the 
same purpose. 

It is often required to maintain a room at one particular 
temperature, and electricity may be employed to give an 
alarm whenever the temperature rises above or falls below 
a certain point. One arrangement for this purpose consists 
of an ordinary thermometer having the top of the mercury 
tube fitted with an air-tight stopper, through which a wire 
is passed down into the tube as far as the mark indicating 
the temperature at which the alarm is desired to sound. 
Another wire is connected with the mercury in the bulb, 
and the free ends of both wires are taken to a suitable 
battery, a continuous-ringing bell being inserted in the 
circuit at some convenient point. If a rise in temperature 
takes place the mercury expands and moves up the tube, 
and at the critical temperature it touches the wire, thus 
completing the circuit and sounding the alarm. This 
arrangement only announces a rise in temperature, but by 
making the thermometer tube in the shape of a letter U an 
alarm may be given also when the temperature falls below 
a certain degree. A device known as a “ thermostat ” is also 
used for the same purpose. This consists of two thin strips 
of unlike metals, such as brass and steel, riveted together 
and suspended between two contact pieces. The two 
metals expand and contract at different rates, so that an 
increase in temperature makes the compound strip bend in 
one direction, and a decrease in temperature makes it bend 
in the opposite direction. When the temperature rises or 
falls beyond a certain limit the strip bends so far as to touch 
one or other of the contact pieces, and the alarm is then 
given. Either of the preceding arrangements can be used 

121 


Electricity 

also as an automatic fire alarm, or if desired matters may be 
arranged so that the closing of the circuit, instead of ring¬ 
ing a bell, turns on or off a lamp, or adjusts a stove, and 
in this way automatically keeps the room at a constant 
temperature. 

Electric alarms operated by ball floats are used to some 
extent for announcing the rise or fall beyond a pre-arranged 
limit of water or other liquids, and there is a very ingenious 
electrical device by which the level of the water in a tank 
or reservoir can be ascertained at any time by indicators 
placed in convenient positions any distance away. 

In factories and other large buildings a watchman is 
frequently employed to make a certain number of rounds 
every night. Being human, a night-watchman would much 
rather sit and snooze over his fire than tramp round a dark 
and silent factory on a cold winter night; and in order to 
make sure that he pays regular visits to every point 
electricity is called in to keep an eye on him. A good 
eight-day clock is fitted with a second dial which is rotated 
by the clockwork mechanism, and a sheet of paper, which 
can be renewed when required, is placed over this dial. 
On the paper are marked divisions representing hours and 
minutes, and other divisions representing the various places 
the watchman is required to visit. A press-button is fixed 
at each point to be visited, and connected by wires with 
the clock and with a battery. As the watchman reaches 
each point on his rounds he presses the button, which is 
usually locked up so that no one else can interfere with it, 
and the current passes round an electro-magnet inside the 
clock case. The magnet then attracts an armature which 
operates a sort of fine-pointed hammer, and a perforation 
is made in the paper, thus recording the exact time at 
which the watchman visited that particular place. 

The current for ordinary electric bells is generally sup- 

122 


Electric Bells and Alarms 

plied by Leclanchd cells, which require little attention, and 
keep in good working order for a very long time. As we 
saw in Chapter IV., these bells soon polarize if used con¬ 
tinuously, but as in bell work they are required to give 
current for short periods only, with fairly long intervals of 
rest, no trouble is caused on this account. These cells 
cannot be used for burglar or other alarms worked on the 
closed-circuit principle, and in such cases some form of 
Daniell cell is usually employed. 


# 


123 


CHAPTER XV 


ELECTRIC CLOCKS 

Amongst the many little worries of domestic life is the 
keeping in order of the various clocks. It ought to be a 
very simple matter to remember to wind up a clock, but 
curiously enough almost everybody forgets to do so now 
and then. We gaze meditatively at the solemn-looking 
machine ticking away on the mantelpiece, wondering 
whether we wound it up last week or not; and we wish 
the wretched thing would go without winding, instead of 
causing us all this mental effort. 

There is usually a way of getting rid of little troubles 
of this kind, and in this case the remedy is to be found in 
an electrically-driven clock. The peculiar feature about 
clocks driven by electricity is that they reverse the order 
of things in key-wound clocks, the pendulum being made 
to drive the clockwork instead of the clockwork driving 
the pendulum. No driving spring is required, and the 
motive power is supplied by a small electro-magnet. 

The actual mechanism varies considerably in different 
makes of clock. In one of the simplest arrangements there 
is a pendulum with an armature of soft iron fixed to the 
extremity of its bob. Below the pendulum is an electro¬ 
magnet, and this is supplied with current from a small 
battery of dry cells. A short piece of metal, called a “pallet,” 
is attached to the rod of the pendulum by means of a 
pivot; and as the pendulum swings it trails this pallet 

124 


Electric Clocks 

backwards and forwards along a horizontal spring. In this 
spring are cut two small notches, one on each side of the 
centre of the swing. As long as the pendulum is swinging 
sufficiently vigorously, the pallet slides over these notches ; 
but when the swing has diminished to a certain point the 
pallet catches in one or other of the notches. This has 
the effect of pressing down the spring so that it touches a 
contact piece just below, and the battery circuit is then 
completed. The electro-magnet now comes into action 
and attracts the armature, thus giving the pendulum a pull 
which sets it swinging vigorously again. The spring is 
then freed from the pressure of the pallet, and it rises to its 
original position, so that the circuit is broken. This puts 
out of action the electro-magnet, and the latter does no 
further work until the pendulum requires another pull. 
The movement of the pendulum drives the wheelwork, 
which is similar to that of an ordinary clock, and the wheel- 
work moves the hands in the usual way. A clock of this 
kind will run without attention for several months, and 
then the battery requires to be renewed. As time-keepers, 
electrically-driven clocks are quite as good as, and often 
very much better than key-wound clocks. 

Everybody must have noticed that the numerous public 
clocks in a large town do not often agree exactly with one 
another, the differences sometimes being quite large; while 
even in one building, such as a large hotel, the different 
clocks vary more or less. This state of things is very 
unsatisfactory, for it is difficult to know which of the clocks 
is exactly right. Although large clocks are made with the 
utmost care by skilled workmen, they cannot possibly be 
made to maintain anything like the accuracy of a high-class 
chronometer, such as is used by navigators ; and the only 
way to keep a number of such clocks in perfect agreement 
is to control their movements from one central or master 

125 


Electricity 

clock. This can be done quite satisfactorily by electricity. 
The master-clock and the various sub-clocks are connected 
electrically, so that a current can be sent from the master- 
clock to all the others. Each sub-clock is fitted with an 
electro-magnet placed behind the figure XII at the top of 
the dial. At the instant when the master-clock reaches the 
hour, the circuit is closed automatically, and the current 
energizes these magnets. The minute hands of all the 
sub-clocks are gripped by the action of the magnets, and 
pulled exactly to the hour; the pulling being backward or 
forward according to whether the clocks are fast or slow. 
In this way all the clocks in the system are in exact agree¬ 
ment at each hour. The same result may be attained by 
adjusting all the sub-clocks so that they gain a little, say a 
few seconds in the hour. In this case the circuit is closed 
about half a minute before the hour. As each sub-clock 
reaches the hour, its electro-magnet comes into action, and 
holds the hands so that they cannot proceed. When the 
master-clock arrives at the hour the circuit is broken, the 
magnets release their captives, and all the clocks move 
forward together. 

It is possible to control sub-clocks so that their pendu¬ 
lums actually beat exactly with the pendulum of the master- 
clock ; but only a small number of clocks can be controlled 
in this way, and they must be of the best quality. The 
method is similar to that used for hourly corrections, the 
main difference being that the circuit is closed by the 
pendulum of the master-clock at each end of its swing, so 
that the pendulums of the sub-clocks are accelerated or 
held back as may be required. 

In the correcting systems already described the sub¬ 
clocks are complete in themselves, so that they work quite 
independently, except at the instant of correction. For 
hotels, schools, and other large buildings requiring clocks 

126 


Electric Clocks 

at a number of different points, a simpler arrangement is 
adopted. Only one complete clock is used, this being the 
master-clock, which may be wound either electrically or by 
key. The sub-clocks are dummies, having only a dial with 
its hands, and an electro-magnetic arrangement behind the 
dial for moving the hands. The sub-clocks are electrically 
connected with the master-clock, and the mechanism of this 
clock is arranged to close the circuit automatically every 
half-minute. Each time this occurs the magnet of each 
sub-clock moves forward the hands half a minute, and in 
this way the dummy clocks are made to travel on together 
by half-minute steps, exactly in unison with the master- 
clock. 


127 


CHAPTER XVI 


THE TELEGRAPH 

We come now to one of the most important inventions of 
the nineteenth century, the electric telegraph. From very 
early times men have felt the necessity for some means of 
rapidly communicating between two distant points. The 
first really practical method of signalling was that of lighting 
beacon fires on the tops of hills, to spread some important 
tidings, such as the approach of an enemy. From this 
simple beginning arose more complicated systems of signal¬ 
ling by semaphore, flags, or flashing lights. All these 
methods proved incapable of dealing with the rapidly 
growing requirements of commerce, for they were far too 
slow in action, and in foggy weather they were of no use 
at all. We are so accustomed to walking into a telegraph 
office, filling up a form, and paying our sixpence or more, 
that it is very difficult for us to realize the immense im¬ 
portance of the electric telegraph ; and probably the best 
way of doing this is to try to imagine the state of things 
which would result if the world’s telegraphic instruments 
were put out of action for a week or two. 

The earliest attempts at the construction of an electric 
telegraph date back to a time long before the discovery of 
the electric current. As early as 1727 it was known that 
an electric discharge could be transmitted to a considerable 
distance through a conducting substance such as a moistened 
thread or a wire, and this fact suggested the possibility of 


The Telegraph 

a method of electric signalling. In 1753 a writer in Scott's 
Magazine brought forward an ingenious scheme based upon 
the attraction between an electrified body and any light 
substance. His telegraph was worked by an electric 
machine, and it consisted of twenty-six separate parallel 
wires, every wire having a metal ball suspended from it at 
each end. Close to each ball was placed a small piece of 
paper upon which was written a letter of the alphabet. 
When any wire was charged, the paper letters at each end 
of it were attracted towards the metal balls, and in this 
way words and sentences were spelled out. Many other 
systems more or less on the same lines were suggested 
during the next fifty years, but although some of them had 
considerable success in an experimental way, they were all 
far too unreliable to have any commercial success. 

With the invention of the voltaic cell, inventors’ ideas 
took a new direction. In 1812a telegraph based upon the 
power of an electric current to decompose water was 
devised by a German named Sommering. He used a 
number of separate wires, each connected to a gold pin 
projecting from below into a glass vessel filled with 
acidulated water. There were thirty-five wires in all, for 
letters and numbers, and when a current was sent along 
any wire bubbles of gas formed at the pin at the end of it, 
and so the letters or numbers were indicated. This tele¬ 
graph, like its predecessors, never came into practical use. 
Oersted’s discovery in 1829 of the production of magnetism 
by electricity laid the foundation of the first really practical 
electric telegraphs, but little progress was made until the 
appearance of the Daniell cell, in 1836. The earlier forms 
of voltaic cells polarized so rapidly that it was impossible 
to obtain a constant current from them, but the non¬ 
polarizing Daniell cell at once removed all difficulty in this 
respect. In the year 1837 three separate practical tele- 
1 129 


Electricity 

graphs were invented: by Morse in the United States, by 
Wheatstone and Cooke in England, and by Steinheil in 
Munich. 

The first telegraph of Wheatstone and Cooke consisted 

of five magnetic needles 
pivoted on a vertical 
dial. The letters of the 
alphabet were marked 
on the dial, and the 
needles were deflected 
by currents made to 
pass through wires by 
the depression of keys, 
so that two needles 
would point towards 
the required letter. 
Fig. 26 is a sketch of 
the dial of this appara¬ 
tus. This telegraph was 
tried successfully on the 
London and North- 
Western Railway, over 
a wire a mile and a half 
in length. Wheatstone 
and Cooke afterwards 
invented a single-needle 
telegraph in which the 
letters were indicated 
by movements of the needle to the right or to the left, 
according to the direction of a current sent through a coil 
of wire. Wheatstone subsequently produced an apparatus 
which printed the letters on paper. 

In the United States, Morse had thought out a scheme 
of telegraphy in 1832, but it was not until 1837 that he got 

130 



Fig. 26.—Dial of Five-Needle Telegraph. 


The Telegraph 

his apparatus into working order. He was an artist by 
profession, and for a long time he was unable to develop 
his ideas for lack of money. After many efforts he suc¬ 
ceeded in obtaining a State grant of ^6000 for the 
construction of a telegraph line between Baltimore and 
Washington, and the first message over this line was sent 
in 1844, the line being thrown open to the public in the 
following year. Amongst the features of this telegraph 
were a receiving instrument which automatically recorded 
the messages on a moving paper ribbon, by means of a 
pencil actuated by an electro-magnet; and an apparatus 
called a relay, which enabled the recording instrument to 
be worked when the current was enfeebled by the resistance 
of a very long wire. Morse also devised a telegraphic 
code which is practically the same as that in use to-day. 

The great discovery of the German Steinheil was that 
a second wire for the return of the current was not necessary, 
and that the earth could be used for this part of the circuit. 

In reading the early history of great inventions one is 
continually struck with the indifference or even hostility 
shown by the general public. In England the electric 
telegraph was practically ignored until the capture of a 
murderer by means of it literally forced the public to see 
its value. The murder was committed near Slough, and 
the murderer succeeded in taking train for London. 
Fortunately the Great Western Railway had a telegraph 
line between Slough and London, and a description tele¬ 
graphed to Paddington enabled the police to arrest the 
murderer on his arrival. In the United States too there 
was just the same indifference. The rate for messages on 
the line between Baltimore and Washington was one cent 
for four words, and the total amount taken during the first 
four days was one cent! 

One of the simplest forms of telegraph is the single- 

131 


Electricity 

needle instrument. This consists of a magnetic needle 
fixed to a spindle at the back of an upright board through 
which the spindle is passed. On the same spindle, but in 
front of the board, is fixed a dial needle, which, of course, 
moves along with the magnetic needle. A coil of wire is 
passed round the magnetic needle, and connected to a 


A 

\/ 

7 

s /// 

S 

\\\ 

commutator for revers¬ 
ing the direction of the 

B 

/ w* 

K 

A / 

T 

/ 

current. By turning a 
handle to the left a 

C 

A A 

L 

\ Ax 

V 

X \ / 

current is made to flow 
through the coil, and 

0 

Ax 

/A 

// 

V 

\X\ / 

the magnetic needle 
moves to one side; but 

E 

\ 

N 

A 

w 

V // 

if the handle is turned 
to the right the current 

F 

\\ A 

0 

/// 

X 

Ax/ 

flows through the coil 
in the opposite direc¬ 

Q 

/A 

P 

\ f/\ 

Y 

/. // 

tion, and the needle 
moves to the other 
side. Instead of a 

H 

\\u 


/A/ 

2 

/Ax 

handle, two keys may 
be used, the movement 

1 \\ 

Fig. 27.—Code 

R xA 

for Single-Needle Telegraph. 

of the needle varying 
according to which key 
is pressed. A good 

at 

the rate 

of 

about 

operator can transmit 
twenty words a minute with this 


instrument. The Morse code, which consists of com¬ 
binations of dots and dashes, is used, a movement of the 
dial needle to the left meaning a dot, and one to the right 
a dash. The code as used in the single-needle instrument 
is shown in Fig. 27. 

Needle instruments are largely used in railway signal 

132 


The Telegraph 

cabins, but for general telegraphic work an instrument 
called the Morse sounder is employed. This consists of 
an electro-magnet which, when a current is passed through 
it, attracts a small piece of iron fixed to one end of a 
pivoted lever. The other end of this lever moves between 
two stops. At the transmitting station the operator closes 
a battery circuit by pressing a key, when the electro-magnet 
of the sounder at the receiving station attracts the iron, 
and the lever flies from one stop to the other with a sharp 
click, returning again as soon as the circuit is broken. A 



Fig. 28.—The Morse Code. 


dot is signalled when the lever falls back immediately after 
the click, and a dash when it makes a short stay before 
returning. Fig. 28 shows the code of signals for the 
Morse telegraph. 

In passing through a very long wire an electric current 
becomes greatly reduced in strength owing to the resistance 
of the wire. If two telegraph stations are a great distance 
apart the energy of the current thus may be unequal to the 
task of making the electro-magnet move the lever of the 
sounder so as to produce a click, but this difficulty is over¬ 
come by the use of an ingenious arrangement called a 
“relay.” It consists of a very small electro-magnet which 

i33 


Electricity 

attracts a light bar, the movement of the bar being made 
to close the circuit of another battery at the receiving 
station. The feeble current works the relay, and the 
current in the local circuit operates the sounder. 

The word “ telegraph,” which is derived from the Greek 
tele , far off, and grapho , I write, strictly signifies writing at 
a distance. The needle instrument and the sounder do not 
write in any way, but by modifying the construction of the 
sounder it can be made to record the messages it receives. 
A small wheel is fitted to the free end of the lever of the 
sounder, and an ink-well is placed so that the wheel dips 
into it when the lever is in the normal position. When 
the circuit is closed the lever moves just as in the ordinary 
sounder, but instead of clicking against a stop it presses 
the inked wheel against a paper ribbon which is kept 
slowly moving forward by clockwork. In this way the 
wheel continues to mark a line along the paper as long as 
the circuit remains closed, and according to the time the 
transmitting key is kept down a short mark or dot, or a 
long mark or dash, is produced. The clockwork which 
moves the paper ribbon is started automatically by the 
current, and it continues working until the message is 
finished. 

A good Morse operator can maintain a speed of about 
thirty words a minute, but this is far too slow for certain 
kinds of telegraphic work, such as the transmission of press 
news, and for such work the Wheatstone automatic trans¬ 
mitter is used. First of all the messages are punched on 
a paper ribbon. This is done by passing the ribbon from 
right to left by clockwork through a punching machine 
which is provided with three keys, one for dots, one for 
dashes, and the other for spaces. If the left-hand key is 
pressed, two holes opposite to one another are made, 
representing a dot; and if the right-hand key is pressed, 

134 


The Telegraph 




Fig. 29.—A Morse Message. 

(a) Perforated Tape. {b) Printed Tape. 


TRANSLATION. 

Series of alternate dots and dashes indicating commencement of message. 

Sec {section) A. D. T. {Daily Telegraph) Fm {from) Bern, Antivan. 

Then follow the letters G. Q., signifying fresh line. 

They hd {had) bn {been) seen advancing in t {the) distance and wr {were) 
recognised by thr {their) usual uniform wh {which) consists o {of) a white fez. 
Finally double dots indicating full stop. 

135 


































































Electricity 

two diagonal holes are punched, representing a dash. In 
Fig. 29, which shows a piece of ribbon punched in this 
way, a third line of holes will be noticed between the out¬ 
side holes representing the dots and dashes. These holes 
are for the purpose of guiding the paper ribbon steadily 
along through the transmitting machine. The punched 
ribbon is then drawn by clockwork through a Wheatstone 
transmitter. In this machine two oscillating needles, con¬ 
nected with one pole of a battery, are placed below the 
moving ribbon. Each time a hole passes, these needles 
make contact with a piece of metal connected with the 
other pole of the battery, thus making and breaking the 
circuit with much greater rapidity than is possible with 
the Morse key. At the receiving station the messages are 
recorded by a form of Morse inker, coming out in dots and 
dashes as though sent by hand. Below the punched ribbon 
in Fig. 29 is shown the corresponding arrangement of dots 
and dashes. The same punched ribbon may be used 
repeatedly when the message has to be sent on a number 
of different lines. The Wheatstone automatic machine is 
capable of transmitting at the rate of from 250 to 400 
words a minute. Fig. 29 is a fragment of a Daily 
Telegraph Balkan War special, as transmitted to the 
Yorkshire Post over the latter’s private wire from London 
to Leeds. In the translation it will be seen that many 
common words are abbreviated. 

One weak point of telegraphy with Wheatstone instru¬ 
ments is that the messages are received in Morse 
code, and have to be translated. During recent years 
telegraphs have been invented which actually produce 
their messages in ordinary written or printed characters. 
A very ingenious instrument is the Hughes printing 
telegraph, which turns out messages in typewritten form. 
Its mechanism is too complicated to be described here, 

136 


The Telegraph 

but in general it consists of a transmitter having a key¬ 
board something like that of a typewriter, by means of 
which currents of electricity are made to press a sheet of 
paper at the right instant against a revolving type-wheel 
bearing the various characters. This telegraph has been 
modified and brought to considerable perfection, and in 
one form or another it is used in European countries and 
in the United States. 

In the Pollak-Virag system of telegraphy the action of 
light upon sensitized photographic paper is utilized. An 
operator punches special groupings of holes on a paper 
ribbon about i inch wide, by means of a perforating 
machine resembling a typewriter, and the ribbon is then 
passed through a machine which transmits by brush con¬ 
tacts. The receiver consists of a very small mirror 
connected to two vibrating diaphragms, which control its 
movements according to the currents received, one dia¬ 
phragm moving the mirror in a vertical direction, and the 
other in a horizontal direction. The mirror reflects a ray 
of light on to photographic bromide paper in the form of a 
moving band about 3 inches in width, and the combined 
action of the two diaphragms makes the mirror move so 
that the ray of light traces out the messages in ordinary 
alphabetical characters. As it moves forward after being 
acted upon by the light, the paper is automatically developed 
and fixed, and then passed through drying rollers. Although 
the writing is rather imperfect in formation it is quite legible 
enough for most messages, but trouble occasionally occurs 
with messages containing figures, owing to confusion arising 
from the similarity of the figures, 3, 5, and 8. The whole 
process is carried out with such rapidity that 40,000 or 
even more words can be transmitted easily in an hour. 

One of the most remarkable of present-day telegraphs 
is the Creed high-speed automatic printing telegraph. 

i37 


Electricity 

This has been devised to do away with hand working as 
far as possible, and to substitute quicker and more accurate 
automatic methods. In this system a perforated paper 
tape is produced by a keyboard perforator at the sending 
station. This tape is just ordinary Wheatstone tape, its 
perforations representing in the Morse code the message to 
be transmitted ; and the main advantage of the Creed per¬ 
forator over the three-key punching machine already 
described lies in the ease and speed with which it can be 
worked. The keyboard contains a separate key for each 
letter or signal of the Morse code, and the pressing of any 
key brings into operation certain punches which make the 
perforations corresponding to that particular letter. The 
perforator can be worked by any one who understands how 
to use an ordinary typewriter, and a speed of about 60 
words a minute can be maintained by a fairly skilful 
operator. If desired a number of tapes may be perforated 
at the same time. 

The tape prepared in this way is passed through a 
Wheatstone transmitter, and long or short currents, accord¬ 
ing to the arrangement of the perforations, are sent out 
along the telegraph line. At the receiving station these 
signals operate a receiving perforator. This machine 
produces another perforated tape, which is an exact copy 
of the tape at the sending station, and it turns out this 
duplicate tape at the rate of from 150 to 200 words a 
minute. There are two forms of this receiving perforator, 
one worked entirely by electricity, and the other by a com¬ 
bination of electricity and compressed air, both forms 
serving the same purpose. The duplicate tape is then 
passed through an automatic printer, which reproduces the 
message in large Roman characters on a paper tape. The 
printer works at a speed of from 80 to about 100 words a 
minute, and the printed tape is pasted on a telegraphic 

138 


on a 


The Telegraph 

form by a semi-automatic process, and the message is then 
ready for delivery. Plate XI. shows a specimen of the 
tape from the receiving perforator, and the corresponding 
translation as turned out by the printer. This message 
formed part of a leading article in the Daily Mail. Some 
idea of the wonderful capabilities of the Creed system may 
be gained from the fact that by means of it practically the 
whole contents of the Daily Mail are telegraphed every 
night from London to Manchester and Paris, for publica¬ 
tion next morninor. 

o 

One of the most remarkable features about present-day 
telegraphy is the ease with which two or more messages 
can be sent simultaneously over one line. Duplex tele¬ 
graphy, or the simultaneous transmission of two separate 
messages in opposite directions over one wire, is now 
practised on almost every line of any importance. At first 
sight duplex telegraphy seems to be an impossibility, for if 
we have two stations, one at each end of a single wire, and 
each station fitted with a transmitter and a receiver, it 
appears as if each transmitter would affect not only the 
receiver at the opposite end of the wire, but also the 
receiver at its own end, thus causing hopeless confusion 
when both transmitters were in use at the same time. 
This actually would be the case with ordinary telegraphic 
methods, but by the use of a special arrangement all con¬ 
fusion in working is avoided. 

We have seen that a magnetic needle is deflected by a 
current passing through a coil of wire placed round it, and 
that the direction in which the needle is deflected depends 
upon the direction of the current in the coil. Now suppose 
we place round the needle two coils of wire, wound so that 
the current in one flows in a direction opposite to that of 
the current in the other. Then, if we pass two equal 
currents, one through each coil, it is evident that they will 

i39 


Electricity 

neutralize one another, so that the needle will not be 
deflected at all. In a duplex system one end of one of 
these coils is connected to earth, say to a copper plate 
buried in the ground, and one end of the other to the line 
wire. The two remaining ends are arranged as branches 
leading off from a single wire connected with the trans¬ 
mitting key. The whole arrangement of coils and needle 
is repeated at the other end of the line. If now the 
transmitting key at station A is pressed, the circuit is closed 
and a current flows along the single wire, and then divides 
into two where the wire branches, half of it taking the path 
through one coil and half the path through the other. 
Equal currents thus flow through the oppositely wound 
coils, and the needle at station A is not deflected. Leaving 
the coils, one of these equal currents flows away to earth, 
while the other passes out along the line wire. On its 
arrival at station B the current is able to pass through only 
one of the coils round the needle, and consequently the 
needle is deflected and the signal given. In this way the 
transmitting operator at station A is able to signal to station 
B without affecting the receiver at his own end, and 
similarly the operator at station B can transmit to A without 
affecting the B receiver. Thus there can be no confusion 
whether the transmitters are worked at different times or 
simultaneously, for each transmitter affects only the 
receiver at the opposite end of the line. The diagram in 
Fig. 30 will help to make clearer the general principle. 
K and K 1 are the two transmitting keys which close the 
circuit, and C and C 1 are the points at which the current 
divides into two. Instead of coils and needles, electro¬ 
magnets operating sounders may be used, such magnets 
having two separate and oppositely wound coils, acting in 
exactly the same way as the coils round the needles. The 
above description is of course only a rough outline of the 

140 


PLATE XT 










































































The Telegraph 

method, and in practice matters are more complicated, 
owing to the necessity for carefully adjusted resistances and 
for condensers. There is also another and different method 
of duplexing a line, but we have not space to describe it. 
Duplex telegraphy requires two operators at each end of 
the line, one to send and the other to receive. 

Diplex telegraphy is the simultaneous transmission of 
two separate messages in the same direction over one line. 
Without going into details it may be said that for this 
purpose two different transmitting keys are required, one of 
which alters the direction, and the other the strength of the 



Fig. 30.—Diagram to illustrate principle of Duplex Telegraphy. 


current though the line wire. The receivers are arranged 
so that one responds only to a strong current, and the other 
only to a current in one particular direction. A line also 
may be quadruplexed, so that it is possible to transmit 
simultaneously two messages from each end, four operators 
being required at each station, two to transmit and two 
to receive. Systems of multiplex telegraphy have been 
devised by which very large numbers of messages can be 
sent at once over a single wire, and the Baudot multiplex 
telegraph has proved very successful. 

The wires for telegraphic purposes may be conveyed 
either above or below the ground. Overground wires are 

141 







Electricity 

carried on poles by means of insulators of porcelain or other 
non-conducting material, protected by a sort of overhanging 
screen. The wires are left bare, and they are generally 
made of copper, but iron is used in some cases. In under¬ 
ground lines the wires formerly were insulated by a covering 
of gutta-percha, but now paper is generally used. Several 
wires, each covered loosely with thoroughly dry paper, are 
laid together in a bundle, the whole bundle or cable being 
enclosed in a strong lead pipe. The paper coverings are 
made to fit loosely so that the wires are surrounded by an 
insulating layer of dry air. As many as 1200 separate 
wires are sometimes enclosed in one pipe. In order to 
keep telegraph lines in working order frequent tests are 
necessary, and the most important British Postal Telegraph 
lines are tested once a week between 7.30 and 7.45 a.m. 
The earth is generally used for the return circuit in 
telegraphy, and the ends of the return wires are connected 
either to metal plates buried in the ground to a depth at 
which the earth is permanently moist, or to iron gas or 
water pipes. The current for telegraph working on a small 
scale is usually supplied by primary cells, the Daniell cell 
being a favourite for this purpose. In large offices the 
current is generally taken from a battery of storage cells. 

During the early days of telegraphy, overhead lines 
were a source of considerable danger when thunderstorms 
were taking place. Lightning flashes often completely 
wrecked the instruments, giving severe shocks to those in 
the vicinity, and in a few cases operators were killed at 
their posts. Danger of this kind is now obviated by the 
use of contrivances known as lightning arresters. There 
are several forms of these, but only one need be mentioned. 
The main features of this are two metal plates separated 
slightly from one another, so that there is a small air gap 
between them. One plate is connected to the line wire, 

142 


The Telegraph 

and the other to earth. Almost all lightning flashes con¬ 
sist of an oscillatory discharge, that is one which passes a 
number of times backwards and forwards between a cloud 
and the earth. A very rapidly alternating discharge of 
this kind finds difficulty in passing along the line wire, 
being greatly impeded by the coils of wire in the various 
pieces of apparatus ; and although the resistance of this 
air gap is very high, the lightning discharge will cross the 
gap sooner than struggle along the line wire. In this way, 
when a flash affects the line, the discharge jumps the gap 
between the plates of the arrester and passes away harm¬ 
lessly to earth, without entering the telegraph office at all. 
As was mentioned in Chapter III., the prevalence of 
magnetic storms sometimes renders telegraph lines quite 
unworkable for a time, but although such disturbances 
cause great delay and general inconvenience, they are not 
likely to be at all dangerous. It is often possible to 
maintain telegraphic communication during magnetic dis¬ 
turbances by using two lines to form a complete metallic 
loop, so that there is no earth return. 


H3 


CHAPTER XVII 


SUBMARINE TELEGRAPHY 

The story of submarine telegraphy is a wonderful record 
of dogged perseverance in the face of tremendous obstacles 
and disastrous failures. It would be of no interest to trace 
the story to its very beginning, and so we will commence 
with the laying of the first cable across the English 
Channel from Dover to Calais, in 1850. A single copper 
wire covered with a layer of gutta-percha half an inch thick 
was used, and leaden weights were attached to it at intervals 
of one hundred yards, the fixing of each weight necessitating 
the stoppage of the cable-laying ship. The line was laid 
successfully, but it failed after working for a single day, and 
it afterwards turned out that a Boulogne fisherman had 
hauled up the cable with his trawl. This line proved that 
telegraphic communication between England and France 
was possible, but the enterprise was assailed with every 
imaginable kind of abuse and ridicule. It is said that some 
people really believed that the cable was worked in the 
style of the old-fashioned house bell, and that the signals 
were given by pulling the wire ! In the next year another 
attempt was made by Mr. T. R. Crampton, a prominent 
railway engineer, who himself contributed half of the 
,£15,000 required. The form of cable adopted by him 
consisted of four copper wires, each covered with two layers 
of gutta-percha, and the four enclosed in a covering formed 
of ten galvanized iron wires wound spirally round them. 

144 


Submarine Telegraphy 

The line proved a permanent success, and this type of 
cable, with certain modifications, is still in use. In 1852 
three attempts were made to connect England and Ireland, 
but the first two failed owing to the employment of cables 
too light to withstand the strong tidal currents, and the 
third was somehow mismanaged as regards the paying-out, 
so that there was not enough cable to reach across. A 
heavier cable was tried in the next year, and this was a 
lasting success. 

The success of these two cables led to the laying of 
many other European cables over similar distances, but we 
must now pass on to a very much bigger undertaking, the 
laying of the Atlantic cable. In 1856 the Atlantic Tele¬ 
graph Company was formed, with the object of establishing 
and working telegraphic communication between Ireland 
and Newfoundland, the three projectors being Messrs. 
J. W. Brett, C. T. Bright, and C. W. Field. The British 
and the United States Governments granted a subsidy, in 
return for which Government messages were to have 
priority over all others, and were to be transmitted free. 
The objections launched against the scheme were of course 
many, some of them making very amusing reading. It is 
however very strange to find so eminent a scientist as 
Professor Airy, then Astronomer Royal, seriously stating 
that it was a mathematical impossibility to submerge a 
cable safely to such depths, and that even if this could be 
done, messages could not be transmitted through such a 
great length of cable. 

It was estimated that a length of about 2500 nautical 
miles would be enough to allow for all contingencies, and 
the construction of the cable was commenced in February 
1857, and completed in June of that year. It is difficult to 
realize the gigantic nature of the task of making a cable of 
such dimensions. The length of copper wire used in 

k 145 


Electricity 

making the conductor was 20,500 miles, while the outer 
sheathing took 367,500 miles of iron wire ; the total length 
of wire used being enough to go round the Earth thirteen 
times. The cable was finally stowed away on board two 
warships, one British and the other American. 

The real troubles began with the laying of the cable. 
After landing the shore end in Valentia Bay, the paying- 
out commenced, but scarcely had five miles been laid when 
the cable caught in the paying-out machinery and parted. 
By tracing it from the shore the lost end was picked up 
and spliced, and the paying-out began again. Everything 
went well for two or three days, and then, after 380 miles 
had been laid, the cable snapped again, owing to some 
mismanagement of the brakes, and was lost at a depth of 
2000 fathoms. The cable had to be abandoned, and the 
ships returned to Plymouth. 

In the next year, 1858, another attempt was made, with 
new and improved machinery and 3000 miles of cable, and 
this time it was decided that the two ships should start 
paying-out from mid-ocean, proceeding in opposite directions 
towards the two shores after splicing their cables. On the 
voyage out the expedition encountered one of the most 
fearful storms on record, which lasted over a week, and the 
British man-of-war, encumbered with the dead weight of 
the cable, came near to disaster. Part of the cable shifted, 
and those on board feared that the whole of the huge mass 
would break away and crash through the vessel’s side. 
Sixteen days after leaving Plymouth the rendezvous was 
reached, the cables were spliced and the ships started. 
After the British ship had paid out 40 miles it was dis¬ 
covered that the cable had parted at some distance from 
the ship, and the vessels once more sought each other, and 
spliced again ready for another effort. This time the cable 
parted after each vessel had paid out a little more than 

146 


Submarine Telegraphy 

ioo miles, and the ships were forced to abandon the 
attempt. 

The failure of this second expedition naturally caused 
great discouragement, and the general feeling was that the 
whole enterprise would have to be given up. The chairman 
of the company recommended that in order to make the 
best of a bad job the remainder of the cable should be sold, 
and the proceeds divided amongst the shareholders, but 
after great efforts on the part of a dauntless few who re¬ 
fused to admit defeat, it was finally decided to make one 
more effort. No time was lost, and on 17th July 1858 
the vessels again sailed from Queenstown. As before, the 
cables were spliced in mid-ocean, and this time, after many 
anxious days, many false alarms, and one or two narrow 
escapes from disaster through faulty pieces of cable dis¬ 
covered almost too late, the cable was landed successfully 
on both shores of the Atlantic early in August. 

The Atlantic cable was now an accomplished fact, and 
dismal forebodings were turned into expressions of ex¬ 
travagant joy. The first messages passed between Queen 
Victoria and the President of the United States, and 
amongst the more important communications was one 
which prevented the sailing from Canada of two British 
regiments which had been ordered to India during the 
Mutiny. In the meantime the Indian Mutiny had been 
suppressed, and therefore these regiments were not required. 
The dispatch of this message saved a sum of about 
,£50,000. The prospects of the cable company seemed 
bright, but after a short time the signals began to grow 
weaker and weaker, and finally, after about seven hundred 
messages had been transmitted, the cable failed altogether. 
This was a great blow to the general public, and we can 
imagine the bitter disappointment of the engineers and 
electricians who had laboured so hard and so long to bring 

HZ 


Electricity 

the cable into being. It was a favourable opportunity for 
the croakers, and amongst a certain section of the public 
doubts were expressed as to whether any messages had 
been transmitted at all. 

A great consultation of experts took place with the 
object of determining the cause of the failure, and the 
unanimous opinion was that the cable had been injured by 
the use of currents of too great intensity. Some years 
elapsed before another attempt could be made, but the 
idea was never abandoned, and a great deal of study was 
given to the problems involved. Mr. Field, the most 
energetic of the original projectors, never relaxed his deter¬ 
mination that the cable should be made a success, and he 
worked incessantly to achieve his ambition. It is said 
that in pursuance of his object he made sixty-four crossings 
of the Atlantic, and considering that he suffered greatly 
from sea-sickness every time this shows remarkable pluck 
and endurance. 

In 1865, new capital having been raised, preparations 
were made for another expedition. It was now decided 
to use only one vessel for laying the cable, and the Great 
Eastern was chosen for the task. This vessel had been 
lying idle for close on ten years, owing to her failure as a 
cargo boat, but her great size and capacity made her most 
suitable for carrying the enormous weight of the whole 
cable. In July 1865 the Great Eastern set sail, under 
the escort of two British warships. When 84 miles had 
been paid out, a fault occurred, and after drawing up about 
10J miles it was found that a piece of iron wire had pierced 
the coating of the cable. The trouble was put right, and 
the paying-out continued successfully until over 700 miles 
had been laid, when another fault appeared. The cable 
was again drawn in until the fault was reached, and 
another piece of iron was found piercing clean through. 

148 


Submarine Telegraphy 

It was evident that two such pieces of iron could not have 
got there by accident, and there was no doubt that they 
had been inserted intentionally by some malicious scoundrel, 
most likely with the object of affecting the company’s 
shares. A start was made once more, and all went well 
until about two-thirds of the distance had been covered, 
when the cable broke and had to be abandoned after 
several nearly successful attempts to recover it. 

In spite of the loss, which amounted to ,£600,000, the 
energetic promoters contrived to raise fresh capital, and in 
1866 the Great Eastern started again. This effort was 
completely successful, and on 28th July 1866 the cable 
was landed amidst great rejoicing. The following extracts 
from the diary of the engineer Sir Daniell Gooch, give us 
some idea of the landing. 

“Is it wrong that I should have felt as though my 
heart would burst when that end of our long line touched 
the shore amid the booming of cannon, the wild, half-mad 
cheers and shouts of the men ? . . . I am given a never- 
dying thought; that I aided in laying the Atlantic cable. 
. . . The old cable hands seemed as though they could 
eat the end ; one man actually put it into his mouth and 
sucked it. They held it up and danced round it, cheering 
at the top of their voices. It was a strange sight, nay, a 
sight that filled our eyes with tears. ... I did cheer, but 
I could better have silently cried.” 

This time the cable was destined to have a long and 
useful life, and later in the same year the 1865 cable was 
recovered, spliced to a new length, and safely brought to 
land, so that there were now two links between the Old 
World and the New. It was estimated that the total cost 
of completing the great undertaking, including the cost of 
the unsuccessful attempts, was nearly two and a half millions 
sterling. Since 1866 cable-laying has proceeded very 

149 


0 

Electricity 

rapidly, and to-day telegraphic communication exists be¬ 
tween almost all parts of the civilized world. According 
to recent statistics, the North Atlantic Ocean is now 
crossed by no less than 17 cables, the number of cables 
all over the world being 2937, with a total length of 
291,137 nautical miles. 

Before describing the actual working of a submarine 
cable, a few words on cable-laying may be of interest. 
Before the cable-ship starts, another vessel is sent over 
the proposed course to make soundings. Galvanized steel 
pianoforte wire is used for sounding, and it is wound in 
lengths of 3 or 4 nautical miles on gun-metal drums. 
The drums are worked by an engine, and the average 
speed of working is somewhere about 100 fathoms a 
minute in descending, and 70 fathoms a minute in picking 
up. Some idea of the time occupied may be gained from 
a sounding in the Atlantic Ocean which registered a depth 
of 3233 fathoms, or nearly 3J miles. The sinker took 
thirty-three minutes fifty seconds in descending, and forty- 
five minutes were taken in picking up. The heavy sinker 
is not brought up with the line, but is detached from the 
sounder by an ingenious contrivance and left at the bottom. 
The sounder is fitted with an arrangement to bring up a 
specimen of the bottom, and also a sample of water; and 
the temperature at any depth is ascertained by self¬ 
registering thermometers. 

When the soundings are complete the cable-ship takes 
up her task. The cable is coiled in tanks on board, and 
is kept constantly under water to prevent injury to the 
gutta-percha insulation by overheating. As each section 
is placed in the tank, the ends of it are led to a test-box, 
and labelled so that they can be easily recognized. Insul¬ 
ated wires run from the test-box to instruments in the 
testing-room, so that the electrical condition of the whole 

150 


Submarine Telegraphy 

cable is constantly under observation. During the whole 
time the cable is being laid its insulation is tested continu¬ 
ously, and at intervals of five minutes signals are sent from 
the shore end to the ship, so that a fault is instantly de¬ 
tected. The cable in its tank is eased out by a number of 
men, and mechanics are posted at the cable drums and 
brakes, while constant streams of water cool the cable and 
the bearings and surfaces of the brakes. The tension, as 
shown by the dynamometer, is at all times under careful 
observation. When it becomes necessary to wind back the 
cable on account of some fault, cuts are made at intervals 
of a quarter or half a mile, tests being made at each cutting 
until the fault is localized in-board. As soon as the cable 
out-board is found “ O.K.,” the ends are spliced up and the 
paying-out begins again. If the cable breaks from any 
cause, a mark-buoy is lowered instantly on the spot, and 
the cable is grappled for. This may take a day or two in 
good weather, but a delay of weeks may be caused by bad 
weather, which makes grappling impossible. 

The practical working of a submarine cable differs in 
many respects from that of a land telegraph line. The 
currents used in submarine telegraphy are extremely small, 
contrary to the popular impression. An insulated cable 
acts like a Leyden jar, in the sense that it accumulates 
electricity and does not quickly part with it, as does a bare 
overhead wire. In the case of a very long cable, such as 
one across the Atlantic, a current continues to flow from it 
for some time after the battery is disconnected. A second 
signal cannot be sent until the electricity is dissipated and 
the cable clear, and if a powerful current were employed 
the time occupied in this clearing would be considerable, so 
that the speed of signalling would be slow. Another 
objection to a powerful current is that if any flaw 
exists in the insulation of the cable, such a current is apt 


Electricity 

to increase the flaw, and finally cause the breakdown of 
the line. 

The feebleness of the currents in submarine telegraphy 
makes it impossible to use the ordinary land telegraph 
receiver, and a more sensitive instrument known as the 
“ mirror receiver ” is used. This consists of a coil of very 
fine wire, in the centre of which a tiny magnetic needle is 
suspended by a fibre of unspun silk. A magnet placed close 
by keeps the needle in one position when no current is 
flowing. As the deflections of the needle are extremely 
small, it is necessary to magnify them in some way, and 
this is done by fixing to the needle a very small mirror, 
upon which falls a ray of light from a lamp. The mirror 
reflects this ray on to a sheet of white paper marked with 
a scale, and as the mirror moves along with the needle the 
point of light travels over the paper, a very small move¬ 
ment of the needle causing the light to travel some inches. 
The receiving operator sits in a darkened room and 
watches the light, which moves to the right or to the left 
according to the direction of the current. The signals 
employed are the same as those for the single-needle 
instrument, a movement to the left indicating a dot, and 
one to the right a dash. In many instruments the total 
weight of magnet and mirror is only two or three grains, 
and the sensitiveness is such that the current from a voltaic 
cell consisting of a lady’s silver thimble with a few drops of 
acidulated water and a diminutive rod of zinc, is sufficient 
to transmit a message across the Atlantic. 

The mirror receiver cannot write down its messages, 
and for recording purposes an instrument invented by Lord 
Kelvin, and called the “siphon recorder,” is used. In this 
instrument a coil of wire is suspended between the poles of 
an electro-magnet, and to it is connected by means of a silk 
fibre a delicate glass tube or siphon. One end of the 

152 


Submarine Telegraphy 

siphon dips into an ink-well, and capillary attraction causes 
the ink to fill the siphon. The other end of the siphon 
almost touches a moving paper ribbon placed beneath it. 
The ink and the paper are oppositely electrified, and the 
attraction between the opposite charges causes the ink to 
spurt out of the siphon in very minute drops, which fall on 
to the paper. As long as no current is passing the siphon 
remains stationary, but when a current flows from the cable 
through the coil, the latter moves to one side or the other, 
according to the direction of the current, and makes the 
siphon move also. Consequently, instead of a straight line 
along the middle of the paper ribbon, a wavy line with 
little peaks on each side of the centre is produced by the 
minute drops of ink. This recorder sometimes refuses to 
work properly in damp weather, owing to the loss of the 
opposite charges on ink and paper, but a later inventor, 
named Cuttriss, has removed this trouble by using a siphon 
kept constantly in vibration by electro-magnetism. The 
ordinary single-needle code is used for the siphon recorder. 


153 


CHAPTER XVIII 


THE TELEPHONE 

In our younger days most of us have amused ourselves 
with a toy telephone consisting of a long piece of string 
having each end passed through the bottom of a little card¬ 
board box, and secured by a knot. If the string is stretched 
tightly this arrangement enables whispered words to be 
heard at a distance of 20 or 30 yards. Simple as is 
this little toy, yet it is probable that many people would 
be rather nonplussed if asked suddenly to explain how the 
sounds travel along the string from one box to the other. 
If the toy had some complicated mechanism most likely 
every one would want to know how it worked, but the whole 
thing is so extremely simple that generally it is dismissed 
without a thought. 

If we strike a tuning-fork and then hold it close to the 
ear, we hear that it produces a sound, and at the same time, 
from a slight sensation in the hand, we become aware that 
the fork is in vibration. As the fork vibrates it disturbs 
the tiny particles of air round it and sets them vibrating, 
and these vibrations are communicated from one particle to 
another until they reach the drum of the ear, when that also 
begins to vibrate and we hear a sound. This is only 
another way of saying that the disturbances of the air 
caused by the vibrations of the tuning-fork are propagated 
in a series of waves, which we call “ sound waves.” Sound is 
transmitted better through liquids than through the air, and 

154 


The Telephone 

better still through solids, and this is why words spoken so 
softly as to be inaudible through the air at a distance of, 
say, ioo feet, can be heard fairly distinctly at that distance 
by means of the string telephone. The sound reaches us 
along the string in exactly the same way as through the air, 
that is, by means of minute impulses passed on from particle 
to particle. 

A more satisfactory arrangement than the string tele¬ 
phone consists of two thin plates of metal connected by a 
wire which is stretched very tightly. Words spoken close 
to one plate are heard by a listener at the other plate up to 
a considerable distance. Let us try to see exactly what 
takes place when this apparatus is used. In the act of 
speaking, vibrations are set up in the air, and these in turn 
set up vibrations in the metal plate. The vibrations are 
then communicated to the wire and to the metal plate at 
the other end, and finally the vibrations of this plate pro¬ 
duce vibrations in the air between the plate and the listener, 
and the sound reaches the ear. 

This simple experiment shows the remarkable fact that 
a plate of metal is able to reproduce faithfully all the vibra¬ 
tions communicated to it by the human voice, and from this 
fact it follows that if we can communicate the vibrations set 
up in one plate by the voice, to another plate at a distance 
of ioo miles, we shall be able to speak to a listener 
at the further plate just as if he were close to us. A 
stretched string or wire transmits the vibrations fairly well 
up to a certain distance, but beyond this distance the vibra¬ 
tions become weaker and weaker until no sound at all 
reaches the air. By the aid of electricity, however, we can 
transmit the vibrations to a tremendous distance, the range 
being limited only by the imperfections of our apparatus. 

The first attempt at the construction of an electric 
telephone, that is an instrument by means of which the 

155 


Electricity 

vibrations set up by the voice or by a musical instrument 
are transmitted by electricity, was made in i860 by Johann 
Philipp Reis, a teacher in a school at Friedrichsdorf, in 
Germany. His transmitting apparatus consisted of a box 
having a hole covered by a tightly stretched membrane, to 
which was attached a little strip of platinum. When the 
membrane was made to vibrate by sounds produced close 
to the box, the strip of platinum moved to and fro against 
a metal tip, which closed the circuit of a battery. The 
receiver was a long needle of soft iron round which was 
wound a coil of wire, and the ends of the needle rested on 

v 

two little bridges of a sounding box. The vibrations of 
the membrane opened and closed the circuit at a great 
speed, and the rapid magnetization of the needle produced 
a tone of the same pitch as the one which set the membrane 
vibrating. This apparatus transmitted musical sounds and 
melodies with great accuracy, but there is considerable 
difference of opinion as to whether it was able to transmit 
speech. Professor Sylvanus Thompson distinctly states 
that Reis’s telephone could and did transmit speech, but 
other experts dispute the fact. We probably shall be quite 
safe in concluding that this telephone did transmit speech, 
but very imperfectly. In any case it is certain that the 
receiver of this apparatus is not based on the same principle 
as the modern telephone receiver. 

Some years later Graham Bell, Professor of Vocal 
Physiology in the University of Boston, turned his attention 
to the electric transmission of speech, probably being led to 
do so from his experiments in teaching the deaf and dumb. 
His apparatuses shown at an exhibition in Philadelphia in 
1876, consisted of a tube having one end open for speaking 
into, and the other closed by a tightly stretched membrane 
to which was attached a very light steel bar magnet. The 
vibrations set up in the membrane by the voice made the 

156 


The Telephone 

little magnet move to and fro in front of the poles of an 
electro-magnet, inserted in a battery circuit, thus inducing 
currents of electricity in the coils of the latter magnet. 
The currents produced in this way varied in direction and 
strength according to the vibratory movements of the 
membrane, and being transmitted along a wire they 
produced similar variations in current in another electro¬ 
magnet in the receiver. The currents produced in this 
manner in the receiver set up vibrations in a metal 
diaphragm in front of the magnet poles, and so the words 
spoken into the transmitter were reproduced. 

Since the year 1876 the telephone has developed with 
remarkable rapidity, and an attempt to trace its growth 
would involve a series of detailed descriptions of closely 
similar inventions which would be quite uninteresting to 
most readers. Now, therefore, that we have introduced 
the instruments, and seen something of its principle and 
its early forms, it will be most satisfactory to omit the 
intermediate stages and to go on to the telephone as used 
in recent years. The first telephone to come into general 
use was the invention of Graham Bell, and was an improved 
form of his early instrument just described. A case or 
tube of ebonite, which forms the handle of the instrument, 
contains a steel bar magnet having a small coil of insulated 
wire at the end nearest the mouthpiece of the tube, the 
ends of the coil passing along the tube to be connected to 
the line wires. Close to the coil end of the magnet, and 
between it and the mouthpiece, is fixed a diaphragm of 
thin sheet-iron. A complete outfit consists of two of these 
instruments connected by wires, and it will be noticed that 
no battery is employed. 

The air vibrations set up by the voice make the 
diaphragm vibrate also, so that it moves backwards and 
forwards. These movements are infinitesimally small, but 

157 


Electricity 

they are sufficient to affect the lines of force of the magnet 
to such an extent that rapidly alternating currents of vary¬ 
ing degrees of strength are set up in the coil and sent along 
the line wire. On arriving at the receiver these currents 
pass through the coil and produce rapid variations in the 
strength of the magnet, so that instead of exerting a 
uniform attraction upon the iron diaphragm, the magnet 
pulls it with constantly varying force, and thus sets it 
vibrating. The air in front of the diaphragm now begins 
to vibrate, and the listener hears a reproduction of the 
words spoken into the transmitter. The way in which the 
fluctuations of the current make the second diaphragm 
vibrate exactly in accordance with the first is very remark¬ 
able, and it is important to notice that the listener does not 
hear the actual voice of the speaker, but a perfect repro¬ 
duction of it; in fact, the second diaphragm speaks. 

The reader probably will be surprised to be told that 
the transmitter and the receiver of a magneto-electric 
telephone are respectively a dynamo and electric motor of 
minute proportions. We provide a dynamo with mechani¬ 
cal motion and it gives us electric current, and by sending 
this current through an electric motor we get mechanical 
motion back again. In the transmitter of the telephone 
just described, the mechanical motion is in the form of 
vibrations of the metal diaphragm, which set up currents of 
electricity in the coil of wire round the magnet, so that the 
transmitter is really a tiny dynamo driven by the voice. 
The receiver is provided with electric current from the 
transmitter, and it converts this into mechanical motion in 
the diaphragm, so that the receiver is a little electric motor. 

Transmitters of the type just described work well over 
short distances, but the currents they produce are too feeble 
for transmission over a very long wire, and on this account 
they have been superseded by transmitters on the micro- 

158 


The Telephone 

phone principle. A microphone is an instrument for 
making extremely small sounds plainly audible. If a 
current is passed through a box containing loose bits of 
broken carbon, it meets with great resistance, but if the 
bits of carbon are compressed their conducting power is 
considerably increased. Even such slight differences in 
pressure as are produced by vibrating the box will affect 
the amount of current passing through the carbon. If this 
current is led by wires to an ordinary telephone receiver 
the arrangement becomes a simple form of microphone. 
The vibrations of the box vary 
the resistance of the carbon, 
and the corresponding varia¬ 
tions in the current set up 
vibrations in the receiver, but 
in a magnified form. The 
smallest sound vibrations alter 
the resistance of the carbon, 
and as these vibrations are 
magnified in the receiver, the 
reproduced sound is magnified Fig. 31.—Diagram of Microphone 
also. The footsteps of a fly Transmitter. 

may be heard quite distinctly by means of a good micro¬ 
phone, and the ticks of a watch sound like the strokes of a 
hammer. 

By means of this power of magnifying vibrations a 
microphone transmitter can be used on a line of tremendous 
length, where an ordinary Bell transmitter would be utterly 
useless. The general features of this transmitter, Fig. 31, 
are a diaphragm and a block of carbon separated slightly 
from one another, the intervening space being filled with 
granules of carbon. These are enclosed in a case of 
ebonite having a mouthpiece in front and two terminals 
behind, one terminal being connected with the carbon block 

i59 












Electricity 

and the other with the diaphragm. From these terminals 
wires are led to a battery and to the receiver, which is of 
the Bell type. The current has to pass through the carbon 
granules, and the movements of the diaphragm when set in 
vibration by the voice vary the pressure upon the granules, 
and in this way set up variations in the current. Carbon 
dust also may be used instead of granular carbon, and then the 

instrument is called a “dust transmitter.” 

It is usual to have a transmitter and 
a receiver on one handle for the greater 
convenience of the user. The arrange¬ 
ment is shown in Fig. 32, and it will be 
seen that when the user places the receiver 
to his ear the transmitting mouthpiece is 
in position for speaking. The microphone 
with its carbon dust is placed at A, just 
below the mouthpiece, and the earpiece 
or receiver B contains a little magnet and 
coil with a diaphragm in front, so that it 
is really a Bell instrument. A little lever 
will be noticed at C. This is a switch 
which brings the transmitter into circuit 
on being pressed with the finger. 

It is now time to see something of the 
arrangement and working of telephone 
systems. As soon as the telephone became a commercially 
practicable instrument the necessity for some means of 
inter-communication became evident, and the telephone 
exchange was brought into being. The first exchange 
was started in 1877, in Boston, but this was a very 
small affair and it was run on very crude lines. When 
one subscriber wished to communicate with another he 
had to call up an operator, who received the message 
and repeated it to the person for whom it was intended ; 

160 



Fig. 32.—Combined 
Telephone Trans¬ 
mitter and Re¬ 
ceiver. 




















The Telephone 

there was no direct communication between the various 
subscribers’ instruments. As the number of users in¬ 
creased it became necessary to devise some system 
whereby each subscriber could call the attention of an 
operator at the central station, and be put into direct 
communication with any other subscriber without delay ; 
and the exchange system of to-day, which fulfils these 
requirements almost to perfection, is the result of gradual 
improvements in telephone methods extending over some 
thirty-five years. 

When a subscriber wishes to telephone, he first must 
call up the operator at the exchange. Until comparatively 
recently this was done by turning a handle placed at the 
side of the instrument. This handle operated a little 
dynamo, and the current produced caused a shutter at the 
exchange to drop and reveal a number, just as in the 
electric bell indicator, so that the operator knew which 
instrument was calling. As soon as the operator answered 
the call, the shutter replaced itself automatically. The 
signal to disconnect was given in the same way, but the 
indicator was of a different colour in order to prevent con¬ 
fusion with a call signal. These handle-operated telephones 
are still in common use, but they are being replaced by 
instruments which do away with handle-turning on the 
part of the subscriber, and with dropping shutters at the 
exchange. In this latest system all that the subscriber has 
to do is to lift his telephone from its rest, when a little 
electric lamp lights up at the exchange ; and when he has 
finished his conversation he merely replaces the telephone, 
and again a little lamp glows. 

We must now see what happens at the exchange when 
a call is made. Each operator has control of a number of 
pairs of flexible cords terminating in plugs, the two cords 
of each pair being electrically connected. The plugs rest 
L 161 


Electricity 

on a shelf in front of the operator, and the cords pass 
through the shelf and hang down below it. If a plug is 
lifted, the cord comes up through the shelf, and it is drawn 
back again by a weight when the plug is not in use. Two 
lamps are provided for each pair of cords, one being fixed 
close to each cord. The two wires leading from each 
subscriber’s instrument are connected to a little tube-shaped 
switch called a “jack,” and each jack has a lamp of its own. 
When a subscriber lifts his telephone from its rest a lamp 
glows, and the operator inserts one plug of a pair into the 
jack thus indicated, and the lamp goes out automatically. 
She then switches on her telephone to the caller and asks 
for the number of the subscriber to whom he wishes to 
speak; and as soon as she gets this she inserts the other 
plug of the pair into the jack belonging to this number. 
By a simple movement she then rings up the required 
person by switching on the current to his telephone bell. 

Here comes in the use of the two lamps connected with 
the cords. As long as the subscribers’ telephones are on 
their rests the lamps are lighted, but as soon as they are 
lifted off the lamps go out. The caller’s telephone is of 
course off its rest, and so the lamp connected with the first 
cord is not lit; but until the subscriber rung up lifts his 
instrument to answer the call, the lamp of the second cord 
remains lit, having first lighted up when the plug was 
inserted in the jack of his number. When the second 
lamp goes out the operator knows that the call has been 
responded to, and that the two subscribers are in com¬ 
munication with each other. Having finished their con¬ 
versation, both subscribers replace their instruments on the 
rests, whereupon both lamps light up, informing the operator 
that she may disconnect by pulling out the plugs. 

It is manifestly impossible for one operator to attend 
to the calls of all the subscribers in the exchange, and so a 

162 


The Telephone 

number of operators are employed, each one having to 
attend to the calls of a certain number of subscribers. At 
the same time it is clear that each operator may be called 
upon to connect one of her subscribers to any other sub¬ 
scriber in the whole exchange. In order to make this 
possible the switchboard is divided into sections, each 
having as many jacks as there are lines in the exchange, so 
that in this respect all the sections are multiples of each 
other, and the whole arrangement is called a “multiple 
switchboard,” the repeated jacks being called “multiple 
jacks.” Then there are other jacks which it is not necessary 
to duplicate. We have seen that when a subscriber calls the 
exchange a lamp glows, and the operator inserts a plug into 
the jack beside the lamp, in order to answer the call and 
ascertain what number is required. These are called 
“ answering jacks,” and the lamp is the line signal. It is 
usual to have three operators to each section of the switch¬ 
board, and each operator has charge of so many answering 
jacks, representing so many subscribers. At the same 
time she has access to the whole section, so that she can 
connect any of her subscribers to any other line in the 
exchange. 

When a number is called for, the operator must be able 
to tell at once whether the line is free or not. The jack 
in her section may be unoccupied, but she must know also 
whether all the multiple jacks belonging to that number 
are free, for an operator at another section may have 
connected the line to one of her subscribers. To enable 
an operator to ascertain this quickly an electrical test is 
provided. When two lines are connected, the whole of the 
multiple jacks belonging to each are charged with electricity, 
and if an operator at any section touches one of these jacks 
with a plug, a current through her receiver makes a click, 
and on hearing the click she knows that the line is engaged. 

163 


Electricity 

The testing takes an extremely short time, and this is why a 
caller receives the reply, “Number engaged,” so promptly 
that he feels inclined to doubt whether the operator has 
made any attempt at all to connect him up to the number. 

In order that an operator may have both hands free to 
manipulate the plugs, her telephone receiver is fixed over 
one ear by a fastening passing over her head, and the 
transmitter is hung from her shoulders so as to be close to 
her mouth. 

In telegraphy it is the rule to employ the earth for the 
return part of the circuit, but this is not customary in 
telephony. The telephone is a much more sensitive 
instrument than the telegraph, and a telephone having an 
earth return is subject to all kinds of strange and weird 
noises which greatly interfere with conversation. These 
noises may be caused by natural electrical disturbances, or 
by the proximity of telegraph and other wires conveying 
electric currents. On this account telephone lines are 
made with a complete metallic circuit. As in telegraphy, 
protection from lightning flashes is afforded by lightning 
arresters. The current for the working of a telephone 
exchange is supplied from a central battery of accumulators, 
and also from dynamos. 

Although the manual exchange telephone system of 
to-day works with remarkable efficiency, it has certain 
weak points. For instance, if an operator cares to do so, 
she can listen to conversations between subscribers, so 
that privacy cannot be assured. As a matter of fact, the 
operators have little time for this kind of thing, at any rate 
during the busy hours of the day, and as a rule they are 
not sufficiently interested in other people’s affairs to make 
any attempt to listen to their remarks. The male operators 
who work through the slack hours of the night are 
occasionally guilty of listening. Some time ago the writer 

164 


PLATE XIT. 



LARGE ELECTRIC TRAVELLING CRANE AT A RAILWAY WORKS. 






























The Telephone 

had to ring up a friend in the very early morning, and 
during the conversation this gentleman asked what time it 
was. Before the writer had time to get a word out, a deep 
bass voice from the exchange replied, “ Half-past two.” 
Little incidents of this sort remind one that it is not wise 
to speak too freely by telephone. Then again operators are 
liable to make wrong connexions through faulty hearing 
of the number called for, and these are equally annoying to 
the caller and to the person rung up in mistake. Many 
other defects might be mentioned, but these are sufficient 
to show that the manual system is not perfect. 

For a long time inventors have been striving to do 
away with all such defects by abolishing the exchange 
operators, and substituting mechanism to work the 
exchanges automatically, and during the last few years the 
system of the Automatic Electric Company, of Chicago, 
has been brought to great perfection. This system is in 
extensive use in the United States, and is employed in 
two or three exchanges in this country. Unfortunately 
the mechanism of this system is extremely complicated, so 
that it is impossible to describe it fully in a book of this 
kind; but some idea of the method of working may be 
given without entering into technical details. 

Each subscriber’s telephone instrument is fitted with a 
dial which turns round on a pivot at its centre. This dial 
has a series of holes round its circumference, numbered 
consecutively from i to 9, and o. Suppose now a 
subscriber wishes to speak to a friend whose telephone 
number is 2583. He removes the receiver from its hook, 
places his finger in the hole marked 2, and turns the dial 
round in a clockwise direction until his finger comes in 
contact with a stop. He then removes his finger, and the 
dial automatically returns to its original position. He then 
places his finger in the hole marked 5, and again turns the 

165 


Electricity 

dial as far as the stop, and when the dial has returned to 
the normal position he repeats the process with his finger 
placed successively in the holes marked 8 and 3. He now 
places the receiver to his ear, and by the time he has done 
this the automatic mechanism at the exchange has made 
the necessary connexions, and has rung the bell of 
subscriber number 2583. On completing the conversation 
each subscriber returns his receiver to its hook, and the 
exchange mechanism returns to its normal position. 

The turning of the dial by the finger coils up a spring, 
and this spring, acting along with a speed governor, makes 
the dial return to its first position at a certain definite 
speed as soon as the finger is removed. During this 
retrograde movement a switch automatically sends out into 
the line a certain number of impulses, the number being 
determined by the hole in which the finger is placed. In 
the case supposed, groups of two, five, eight, and three 
impulses respectively would be sent out, each group 
separated from the next by an interval during which the 
subscriber is turning the dial. 

Now let us see what takes place at the exchange. 
The subscriber’s instrument is connected to a mechanical 
arrangement known as a “ line switch.” This switch 
is brought into play by the act of removing the receiver 
from its hook, and it then automatically connects the 
subscriber’s line to what is called a “first selector” switch. 
The group of two impulses sent out by the first turning of 
the dial raises this first selector two steps, and it then 
sweeps along a row of contacts connected to “trunks” 
going to the 2000 section. Passing by occupied trunks, it 
finds an idle one, and so connects the line to an idle 
“second selector.” This selector is operated by the second 
group of impulses, five in number, and after being raised 
five steps it acts like the first selector, and finds an idle 

166 


The Telephone 

trunk leading to the 2500 section. This places the caller’s 
line in connexion with still another switch called a 
“connector,” and this switch, operated by the remaining 
groups of eight and three impulses, finds the required tens 
section, and selects the third member of that section. If 
the number 2583 is disengaged, the connector switch now 
sends current from the central battery to this instrument, 
thus ringing its bell, and it also supplies speaking current 
to the two lines during the conversation, restores the 
exchange mechanism to its original condition as soon as 
the conversation is ended and the subscribers have hunof 
up their receivers, and registers the call on the calling 
subscriber’s meter. If the connector finds the number 
engaged, it sends out an intermittent buzzing sound, to 
inform the caller of the fact. All these operations take 
time to describe, even in outline, but in practice they are 
carried out with the utmost rapidity, each step in the con¬ 
necting-up process taking only a small fraction of a second. 

For ordinary local calls the automatic system requires 
no operators at all, but for the convenience of users there 
are usually two clerks at the exchange, one to give 
any information required by subscribers, and the other to 
record complaints regarding faulty working. For trunk 
calls, the subscriber places his finger in the hole marked o, 
and gives the dial one turn. This connects him to an 
operator at the trunk switchboard, who makes the required 
connexion and then calls him up in the usual way. 

It might be thought that the complex mechanism of an 
automatic exchange would constantly be getting out of 
order, but it is found to work with great smoothness. 
Each automatic switchboard has a skilled electrician in 
attendance, and he is informed instantly of any faulty 
working by means of supervisory lamps and other signals. 
Even without these signals the attendant would be quickly 

167 


Electricity 

aware of any breakdown, for his ear becomes so accustomed 
to the sounds made by the apparatus during the connecting- 
up, that any abnormal sound due to faulty connecting 
attracts his attention at once. However detected, the 
faults are put right immediately, and it often happens that 
a defective line is noted and repaired before the subscriber 
knows that anything is wrong. 

On account of its high speed in making connexions 
and disconnexions, its absolute accuracy, and its privacy, 
the automatic telephone system has proved most popular 
wherever it has been given a fair trial. Its advantages are 
most obvious in large city exchanges where the traffic 
during business hours is tremendously heavy, and it is 
probable that before very long the automatic system will 
have replaced manual methods for all such exchanges. 

The telephone system is more highly developed in the 
United States than in this country, and some of the 
exchanges have been made to do a great deal more than 
simply transmit messages. For instance, in Chicago there 
is a system by which a subscriber, on connecting himself to 
a special circuit, is automatically informed of the correct 
time, by means of phonographs, between the hours of 8 
a.m. and io p.m. New York goes further than this how¬ 
ever, and has a regular system of news circulation by tele¬ 
phone. According to Electricity , the daily programme is 
as follows: “8 a.m., exact astronomical time; 8 to 9 a.m., 
weather reports, London Stock Exchange news, special 
news item ; 9 to 9.30 a.m., sales, amusements, business 
events; 9.45 to 10 a.m., personal news, small notices; 10 
to 10.30 a.m., New York Stock Exchange and market 
news; 11.30 a.m. to 12 noon, local news, miscellaneous; 
12 noon, exact astronomical time, latest telegrams, military 
and parliamentary news; 2 to 2.15 p.m., European cables; 
1.15 to 2.30 p.m., Washington news; 2.30 to 2.45 p.m., 

168 


The Telephone 

fashions, ladies’ news; 2.45 to 3.15 p.m., sporting and 
theatrical news ; 3.15 to 3.30 p.m., closing news from Wall 
Street; 3.30 to 5 p.m., musical news, recitals, etc. ; 5 to 6 
p.m., feuilleton sketches, literary news ; 8 to 10.30 p.m., 
selected evening performance—music, opera, recitations.” 
Considering the elaborate nature of this scheme one might 
imagine that the subscription would be high, but as a 
matter of fact it is only six shillings per month. 

The telephone has proved of great value in mine rescue 
work, in providing means of communication between the 
rescue party and those in the rear. This end is achieved 
by means of a portable telephone, but as the members of a 
rescue party often wear oxygen helmets, the ordinary tele¬ 
phone mouthpiece is of no use. To overcome this difficulty 
the transmitter is fastened round the throat. The vibra¬ 
tions of the vocal cords pass through the wall of the throat, 
and thus operate the transmitter. The receiver is fixed 
over one ear by means of suitable head-gear, and the con¬ 
necting wire is laid by the advancing rescuers. A case 
containing some hundreds of feet of wire is strapped round 
the waist, and as the wearer walks forward this wire pays 
itself out automatically. 

By the time that the telephone came to be a really 
practical instrument, capable of communicating over long 
distances on land, the Atlantic telegraph cable was in 
operation, and an attempt was made to telephone from one 
continent to the other by means of it, but without success. 
In speaking of submarine telegraphy in Chapter XVII. we 
saw that the cable acts like a Leyden jar, and it was this 
fact that made it impossible to telephone through more than 
about 20 miles of cable, so that transatlantic telephony 
was quite out of the question. It was evident that little 
progress could be made in this direction unless some means 
could be devised for neutralizing this capacity effect, as it 

169 


Electricity 

is called, of the cable, and finally it was discovered that 
this could be done by inserting at intervals along the cable 
a number of coils of wire. These coils are known as “load¬ 
ing coils,” and a cable provided with them is called a “ loaded 
cable.” Such cables have been laid across various narrow 
seas, such as between England and France, and England 
and Ireland, and these have proved very successful for 
telephonic communication. The problem of transatlantic 
telephony however still remains to be solved. Experi¬ 
ments have been made in submarine telephony over a bare 
iron cable, instead of the usual insulated cable. Conversa¬ 
tions have been carried on in this way without difficulty 
between Seattle, Washington, U.S.A., and Vashon 
Island, a total distance of about n miles, and it is 
possible that uninsulated cables may play an extremely 
important part in the development of submarine telephony. 


CHAPTER XIX 


SOME TELEGRAPHIC AND TELEPHONIC 

INVENTIONS 

In telegraphy messages not only may be received, but also 
recorded, by the Morse printer or one of its modifications, 
but in ordinary telephony there is no mechanical method of 
recording messages. This means that we can communicate 
by telephone only when we can call up somebody to receive 
the message at the other end, and if no one happens to be 
within hearing of the telephone bell we are quite helpless. 
This is always annoying, and if the message is urgent the 
delay may be serious. Several arrangements for over¬ 
coming this difficulty by means of automatic recording 
mechanism have been invented, but the only really suc¬ 
cessful one is the telegraphone. 

This instrument is the invention of Waldemar Poulsen, 
whose apparatus for wireless telegraphy we shall speak of 
in the next chapter. The telegraphone performs at the 
same time the work of a telephone and of a phonograph. 
In the ordinary type of phonograph the record is made in 
the form of depressions or indentations on the surface of a 
cylinder of wax ; these indentations being produced by a 
stylus actuated by vibrations set up in a diaphragm by the 
act of speaking. In the telegraphone the same result is 
obtained entirely by electro-magnetic action. The wax 
cylinder of the phonograph is replaced by a steel wire or 
ribbon, and the recording stylus by an electro-magnet. 

171 


Electricity 

The steel ribbon is arranged to travel along over two 
cylinders or reels kept in constant rotation, and a small 
electro-magnet is fixed midway between the cylinders so 
that the ribbon passes close above it. This magnet is 
connected to the telephone line, so that its magnetism 
fluctuates in accordance with the variations in the current 
in the line. We have seen that steel retains magnetism 
imparted to it. In passing over the electro-magnet the 
steel ribbon is magnetized in constantly varying degrees, 
corresponding exactly with the variations in the line current 
set up by the speaker’s voice, and these magnetic impres¬ 
sions are retained by the ribbon. When the speaker has 
finished, the telephone line is disconnected, the ribbon is 
carried back to the point at which it started, and the 
apparatus is connected to ^the telephone receiver. The 
ribbon now moves forward again, and this time it acts like 
the speaker’s voice, the varying intensity of its magnetic 
record producing corresponding variations in the strength 
of the magnet, so causing the receiver diaphragm to repro¬ 
duce the sounds in the ordinary way. 

The magnetic record made in this manner is fairly 
permanent, and if desired it may be reproduced over and 
over again. In most cases, however, a permanent record 
is of no value, and so the magnetic impressions are 
obliterated in order that the ribbon may be used to take 
a new record. This can be done by passing a permanent 
magnet along the ribbon, but it is more convenient to have 
an automatic obliterating arrangement. This consists of 
another electro-magnet fixed close to the recording magnet, 
so that the ribbon passes over it before reaching the latter. 
The obliterating magnet is connected with a battery, and 
its unvarying magnetism destroys all traces of the previous 
record, and the ribbon passes forward to the recording 
magnet ready to receive new impressions. 

172 


Telegraphic and Telephonic Inventions 

For recording telephone messages the telegraphone is 
attached to the telephone instrument, and by automatically 
operated switches it is set working by a distant speaker. 
It records all messages received during the absence of its 
owner, who, on his return, connects it to his receiver, and 
thus hears a faithful reproduction of every word. By 
speaking into his instrument before going out, the owner 
can leave a message stating the time at which he expects 
to return, and this message will be repeated by the tele¬ 
graphone to anybody ringing up in the meantime. The 
most recent forms of telegraphone are capable of recording 
speeches over an hour in length, and their reproduction is 
as clear as that of any phonograph, indeed in many respects 
it is considerably more perfect. 

Another electrical apparatus for recording speech may 
be mentioned. This rejoices in the uncouth name of the 
Photographophone, and it is the invention of Ernst 
Ruhmer, a German. Its working is based upon the fact 
that the intensity of the light of the electric arc may be 
varied by sound vibrations, each variation in the latter 
producing a corresponding variation in the amount of light. 
In the photographophone the light of an arc lamp is passed 
through a lens which focuses it upon a moving photographic 
film. By speaking or singing, the light is made to vary in 
brilliance, and proportionate effects are produced in the 
silver bromide of the film. On developing the film a 
permanent record of the changes in the light intensity is 
obtained, in the form of shadings of different degrees of 
darkness. The film is now moved forward from end to 
end in front of a fairly powerful lamp. The light passes 
through the film, and falls upon a sort of plate made of 
selenium. This is a non-metallic substance which possesses 
the curious property of altering its resistance to an electric 
current according to the amount of light falling upon it; 

i73 


Electricity 

the greater the amount of light, the more current will the 
selenium allow to pass. The selenium plate is connected 
with a telephone receiver and with a battery. As the film 
travels along, its varying shadings allow an ever-changing 
amount of light to pass through and fall upon the selenium, 
which varies its resistance accordingly. The resulting 
variations in the current make the receiver diaphragm give 
out a series of sounds, which are exact reproductions of the 
original sounds made by the voice. The reproduction of 
speech by the photographophone is quite good, but as a 
rule it is not so perfect as with the telegraphone. 

About ten years ago a German inventor, Professor A. 
Korn, brought out the first really practical method of 
telegraphing drawings or photographs. This invention is 
remarkable not only for what it accomplishes, but perhaps 
still more for the ingenuity with which the many peculiar 
difficulties of the process are overcome. Like the photo¬ 
graphophone, Korn’s photo-telegraphic apparatus utilizes 
the power of selenium to alter its resistance with the amount 
of light reaching it. 

Almost everybody is familiar with the terms “positive” 
and “ negative ” as used in photography. The finished paper 
print is a positive, with light and shade in the correct 
positions ; while the glass plate from which the print is made 
is a negative, with light and shade reversed. The lantern 
slide also is a positive, and it is exactly like the paper print, 
except that it has a base of glass instead of paper, so that 
it is transparent. Similarly, a positive may be made on a 
piece of celluloid, and this, besides being transparent, is 
flexible. The first step in transmitting on the Korn system 
is to make from the photograph to be telegraphed a positive 
of this kind, both transparent and flexible. This is bent 
round a glass drum or cylinder, and fixed so that it cannot 
possibly move. The cylinder is given a twofold move- 

174 


Telegraphic and Telephonic Inventions 

ment. It is rotated by means of an electric motor, and at 
the same time it is made to travel slowly along in the 
direction of its length. In fact its movement is very 
similar to that of a screw, which turns round and moves 
forward at the same time. A powerful beam of light is 
concentrated upon the positive. This beam remains 
stationary, but owing to the dual movement of the cylinder 
it passes over every part of the positive, following a spiral 
path. Exactly the same effect would be produced by 
keeping the cylinder still and moving the beam spirally 
round it, but this arrangement would be more difficult to 
manipulate. The forward movement of the cylinder is 
extremely small, so that the spiral is as fine as it is possible 
to get it without having adjacent lines actually touching. 
The light passes through the positive into the cylinder, and 
is reflected towards a selenium cell ; and as the positive 
has an almost infinite number of gradations of tone, or 
degrees of light and shade, the amount of light reaching 
the cell varies constantly all the time. The selenium 
therefore alters its resistance, and allows a constantly 
varying current to pass through it, and so to the trans¬ 
mission line. 

At the receiving end is another cylinder having the 
same rotating and forward movement, and round this is 
fixed a sensitive photographic film. This film is protected 
by a screen having a small opening, and no light can reach 
it except through this aperture. The incoming current is 
made to control a beam of light focused to fall upon the 
screen aperture, the amount of light varying according to 
the amount of current. In this way the beam of light, like 
the one at the transmitting end, traces a spiral from end to 
end of the film, and on developing the film a reproduction 
of the original photograph is obtained. The telegraphed 
photograph is thus made up of an enormous number 

175 


Electricity 

of lines side by side, but these are so close to one 
another that they are scarcely noticed, and the effect is 
something like that of a rather coarse-grained ordinary 
photograph. 

It is obvious that the success of this method depends 
upon the maintaining of absolute uniformity in the motion 
of the two cylinders, and this is managed in a very ingenious 
way. It will be remembered that one method of securing 
uniformity in a number of sub-clocks under the control of 
a master-clock is that of adjusting the sub-clocks to go a 
little faster than the master-clock. Then, when the sub¬ 
clocks reach the hour, they are held back by electro¬ 
magnetic action until the master-clock arrives at the hour, 
when all proceed together. 

A similar method is employed for the cylinders. They 
are driven by electric motors, and the motor at the re¬ 
ceiving end is adjusted so as to run very slightly faster 
than the motor at the sending end. The result is that 
the receiving cylinder completes one revolution a minute 
fraction of a second before the transmitting cylinder. It 
is then automatically held back until the sending cylinder 
completes its revolution, and then both commence the next 
revolution exactly together. The pause made by the 
receiving cylinder is of extremely short duration, but in 
order that there shall be no break in the spiral traced by 
light upon the film, the pause takes place at the point 
where the ends of the film come together. In actual 
practice certain other details of adjustment are required 
to ensure precision in working, but the main features of 
the process are as described. 

Although the above photo-telegraphic process is very 
satisfactory in working, it has been superseded to some 
extent by another process of a quite different nature. By 
copying the original photograph through a glass screen 

176 


Telegraphic and Telephonic Inventions 

covered with a multitude of very fine parallel lines, a half¬ 
tone reproduction is made. This is formed of an immense 
number of light and dark lines of varying breadth, and it 
is printed in non-conducting ink on lead-foil, so that while 
the dark lines are bare foil, the light ones are covered with 
the ink. This half-tone is placed round a metal cylinder 
having the same movement as the cylinders in the previous 
processes, and a metal point, or “stylus” as it is called, is 
made to rest lightly upon the foil picture, so that it travels 
all over it, from one end to the other. An electrical circuit 
is arranged so that when the stylus touches a piece of the 
bare foil a current is sent out along the line wire. This 
current is therefore intermittent, being interrupted each 
time the stylus passes over a part of the half-tone picture 
covered with the non-conducting ink, the succeeding 
periods of current and no current varying with the breadth 
of the conducting and the non-conducting lines. This 
intermittent current goes to a similar arrangement of 
stylus and cylinder at the receiving end, this cylinder 
having round it a sheet of paper coated with a chemical 
preparation. The coating is white all over to begin with, 
but it turns black wherever the current passes through it. 
The final result is that the intermittent current builds up 
a reproduction in black-and-white of the original photo¬ 
graph. In this process also the cylinders have to be 
“synchronized,” or adjusted to run at the same speed. 
Both this process and the foregoing one have been used 
successfully for the transmission of press photographs, 
notably by the Daily Mirror . 

Professor Korn has carried out some interesting and 
fairly successful experiments in wireless transmission of 
photographs, but as yet the wireless results are consider¬ 
ably inferior to those obtained with a line conductor. For 
transmitting black-and-white pictures, line drawings, or 
M 177 


Electricity 

autographs by wireless, a combination of the two methods 
just mentioned is employed ; the second method being 
used for sending, and the first or selenium method for 
receiving. For true half-tone pictures the selenium method 
is used at each end. 


178 


CHAPTER XX 


WIRELESS TELEGRAPHY AND TELEPHONY- 
PRINCIPLES AND APPARATUS 

Wireless telegraphy is probably the most remarkable and 
at the same time the most interesting of all the varied 
applications of electricity. The exceptional popular 
interest in wireless communication, as compared with most 
of the other daily tasks which electricity is called upon 
to perform, is easy to understand. The average man does 
not realize that although we are able to make electricity 
come and go at our bidding, we have little certain know¬ 
ledge of its nature. He is so accustomed to hearing of 
the electric current, and of the work it is made to do, that 
he sees little to marvel at so long as there is a connecting 
wire. Electricity is produced by batteries or by a dynamo, 
sent along a wire, and made to drive the necessary 
machinery; apparently it is all quite simple. But take 
away the connecting wire, and the case is different. In 
wireless telegraphy electricity is produced as usual, but 
instantly it passes out into the unknown, and, as far as 
our senses can tell, it is lost for ever. Yet at some 
distant point, hundreds or even thousands of miles away, 
the electrical influence reappears, emerging from the 
unknown with its burden of words and sentences. There 
is something uncanny about this, something suggesting 
telepathy and the occult, and herein lies the fascination of 
wireless telegraphy. 


179 


Electricity 

The idea of communicating without any connecting 
wires is an old one. About the year 1842, Morse, of tele¬ 
graph fame, succeeded in transmitting telegraphic signals 
across rivers and canals without a connecting wire. His 
method was to stretch along each bank of the river a wire 
equal in length to three times the breadth of the river. 
One of these wires was connected with the transmitter and 
with a battery, and the other with a receiver, both wires 
terminating in copper plates sunk in the water. In this 
case the water took the place of a connecting wire, and 
acted as the conducting medium. A few years later 
another investigator, a Scotchman named Lindsay, suc¬ 
ceeded in telegraphing across the river Tay, at a point 
where it is over a mile and a half wide, by similar methods. 
Lindsay appears to have been the first to suggest the possi¬ 
bility of telegraphing across the Atlantic, and although at 
that time, 1845, the idea must have seemed a wild one, he 
had the firmest faith in its ultimate accomplishment. 

Amongst those who followed Lindsay’s experiments 
with keen interest was the late Sir William, then Mr. 
Preece, but it was not until 1882, twenty years after 
Lindsay’s death, that he commenced experiments on his 
own account. In March of that year the cable across the 
Solent failed, and Preece took the opportunity of trying to 
signal across without a connecting wire. He used two 
overhead wires, each terminating in large copper plates 
sunk in the sea, one stretching from Southampton to 
Southsea Pier, and the other from Ryde Pier to Sconce 
Point. The experiment was successful, audible Morse 
signals being received on each side. In this experiment, 
as in those of Morse and Lindsay, the water acted as the 
conducting medium; but a year or two later, Preece 
turned his attention to a different method of wireless com¬ 
munication, by means of induction. This method was 

180 


Wireless Telegraphy and Telephony 

based upon the fact that at the instant of starting and 
stopping a current in one wire, another current is induced 
in a second wire placed parallel to it, even when the two 
wires are a considerable distance apart. Many successful 
experiments in this induction telegraphy were made, one 
of the most striking being that between the Island of Mull 
and the mainland, in 1895. The cable between the island 
and the mainland had broken, and by means of induction 
perfect telegraphic communication was maintained during 
the time that the cable was being repaired. Although this 
system of wireless telegraphy is quite successful for short 
distances, it becomes impracticable when the distance is 
increased, because the length of each of the two parallel 
wires must be roughly equal to the distance between them. 
These experiments of Preece are of great interest, but we 
must leave them because they have little connexion with 
present-day wireless telegraphy, in which utterly different 
methods are used. 

All the commercial wireless systems of to-day depend 
upon the production and transmission of electric waves. 
About the year 1837 it was discovered that the discharge 
of a Leyden jar did not consist of only one sudden rush of 
electricity, but of a series of electric oscillations, which 
surged backwards and forwards until electric equilibrium 
was restored. This discovery was verified by later 
experimenters, and it forms the foundation of our knowledge 
of electric waves. At this point many readers probably 
will ask, “What are electric waves?” It is impossible to 
answer this question fully, for we still have a great deal to 
learn about these waves, and we only can state the con¬ 
clusions at which our greatest scientists have arrived after 
much thought and many experiments. It is believed that 
all space is filled with a medium to which the name 
“ether” has been given, and that this ether extends 

181 


Electricity 

throughout the matter. We do not know what the ether 
is, but the important fact is that it can receive and transmit 
vibrations in the form of ether waves. There are different 
kinds of ether waves, and they produce entirely different 
effects. Some of them produce the effect which we call 
light, and these are called “light waves.” Others produce 
the effect known as heat, and they are called “ heat waves ” ; 
and still others produce electricity, and these we call 
“electric waves.” These waves travel through the ether at 
the enormous speed of 186,000 miles per second, so that 
they would cross the Atlantic Ocean in about ^ second. 
The fact that light also travels at this speed suggested that 
there might be some connexion between the two sets of 
waves, and after much experiment it has been demonstrated 
that the waves of light and electricity are identical except 
in their length. 

Later on in this chapter we shall have occasion to refer 
frequently to wave-length, and we may take this opportunity 
of explaining what is understood by this term. Wave¬ 
length is the distance measured from the crest of one wave 
to the crest of the next, across the intervening trough or 
hollow. From this it will be seen that the greater the 
wave-length, the farther apart are the waves; and also that 
if we have two sets of waves of different wave-lengths but 
travelling at the same speed, then the number of waves 
arriving at any point in one second will be greater in the 
case of the shorter waves, because these are closer together. 

A tuning-fork in vibration disturbs the surrounding air, 
and sets up air waves which produce the effect called sound 
when they strike against the drums of our ears. In a 
similar way the discharge of a Leyden jar disturbs the 
surrounding ether, and sets up electric ether waves ; but 
these waves produce no effect upon us in the shape of sight, 
sound, or feeling. There is however a very simple piece 

182 


Wireless Telegraphy and Telephony 

of apparatus which acts as a sort of electric eye or ear, and 
detects the waves for us. This consists of a glass tube 
loosely filled with metal filings, and having a cork at each 
end. A wire is passed through each cork so as to project 
well into the tube, but so that the two ends do not touch 
one another, and the outer ends of these wires are con¬ 
nected to a battery of one or two cells, and to some kind of 
electrically worked apparatus, such as an electric bell. So 
long as the filings lie quite loosely in the tube they offer 
a very high resistance, and no current passes. If now 
electric waves are set up by the discharge of a Leyden jar, 
these waves fall upon the tube and cause the resistance 
of the filings to decrease greatly. The filings now form a 
conducting path through which the current passes, and so 
the bell rings. If no further discharge takes place the 
electric waves cease, but the filings do not return to their 
original highly resistant condition, but retain their con¬ 
ductivity, and the current continues to pass, and the bell 
goes on ringing. To stop the bell it is only necessary 
to tap the tube gently, when the filings immediately fall 
back into their first state, so that the current cannot pass 
through them. 

Now let us see how the “coherer,” as the filings tube is 
called, is used in actual wireless telegraphy. Fig. 33# 
shows a simple arrangement for the purpose. A is an 
induction coil, and B the battery supplying the current. 
The coil is fitted with a spark gap, consisting of two 
highly polished brass balls CC, one of these balls being 
connected to a vertical wire supported by a pole, and the 
other to earth. D is a Morse key for starting and stopping 
the current. When the key is pressed down, current flows 
from the battery to the coil, and in passing through the 
coil it is raised to a very high voltage, as described in 
Chapter VIII. This high tension current is sent into the 

183 


Electricity 

aerial wire, which quickly becomes charged up to its 
utmost limits. But more current continues to arrive, and 
so the electricity in the aerial, unable to bear any longer 
the enormous pressure, takes the only path of escape and 




Fig. 33. —Diagram of simple Wireless Transmitting and Receiving Apparatus. 


bursts violently across the air gap separating the brass 
balls. Surging oscillations are then produced in the aerial, 
the ether is violently disturbed, and electric waves are 
set in motion. This is the transmitting part of the 
apparatus. 

If a stone is dropped into a pond, little waves are set in 

184 










































Wireless Telegraphy and Telephony 

motion, and these spread outwards in ever-widening rings. 
Electric waves also are propagated outwards in widening 
rings, but instead of travelling in one plane only, like the 
water waves, they proceed in every plane ; and when they 
arrive at the receiving aerial they set up in it oscillations 
of the same nature as those which produced the waves. 
Let us suppose electric waves to reach the aerial wire of 
Fig. 33 b. The resistance of the coherer H is at once lowered 
so that current from battery N flows and operates the relay 
F, which closes the circuit of battery M. This battery 
has a twofold task. It operates the sounder E, and it 
energizes the electro-magnet of the de-coherer K, as shown 
by the dotted lines. This de-coherer is simply an electric 
bell without the gong, arranged so that the hammer strikes 
the coherer tube; and its purpose is to tap the tube 
automatically and much more rapidly than is possible by 
hand. The sounder therefore gives a click, and the de¬ 
coherer taps the tube, restoring the resistance of the 
filings. The circuit of battery N is then broken, and the 
relay therefore interrupts the circuit of battery M. If 
waves continue to arrive, the circuits are again closed, 
another click is given, and again the hammer taps the 
tube. As long as waves are falling upon the aerial, the 
alternate makings and breakings of the circuits follow one 
another very rapidly and the sounder goes on working. 
When the waves cease, the hammer of the de-coherer has 
the last word, and the circuits of both batteries remain 
broken. To confine the electric waves to their proper 
sphere two coils of wire, LL, called choking coils, are 
inserted as shown. 

In this simple apparatus we have all the really essential 
features of a wireless installation for short distances. For 
long distance work various modifications are necessary, 
but the principle remains exactly the same. In land wire- 

185 


Electricity 

less stations the single vertical aerial wire becomes an 
elaborate arrangement of wires carried on huge masts and 
towers. The distance over which signals can be trans¬ 
mitted and received depends to a considerable extent upon 
the height of the aerial, and consequently land stations 
have the supporting masts or towers from one to several 
hundred feet in height, according to the range over which 
it is desired to work. As a rule the same aerial is used both 
for transmitting and receiving, but some stations have a 
separate aerial for each purpose. A good idea of the 
appearance of commercial aerials for long distance working 
may be obtained from the frontispiece, which shows the 
Marconi station at Glace Bay, Nova Scotia, from which 
wireless communication is held with the Marconi station at 
Clifden, in Galway, Ireland. 

In the first wireless stations what is called a “plain 
aerial ” transmitter was used, and this was almost the same 
as the transmitting apparatus in Fig. 33#, except, of course, 
that it was on a larger scale. This arrangement had many 
serious drawbacks, including that of a very limited range, 
and it has been abandoned in favour of the “ coupled ” 
transmitter, a sketch of which is shown in Fig. 34. In this 
transmitter there are two separate circuits, having the same 
rate of oscillation. A is an induction coil, supplied with 
current from the battery B, and C is a condenser. A 
condenser is simply an apparatus for storing up charges of 
electricity. It may take a variety of forms, but in every 
case it must consist of two conducting layers separated by 
a non-conducting layer, the latter being called the 
“dielectric.” The Leyden jar is a condenser, with con¬ 
ducting layers of tinfoil and a dielectric of glass, but the 
condensers used for wireless purposes generally consist of 
a number of parallel sheets of metal separated by glass or 
mica, or in some cases by air only. The induction coil 


Wireless Telegraphy and Telephony 

charges up the condenser with high tension electricity, until 
the pressure becomes so great that the electricity is 
discharged in the form of a spark between the brass balls 
of the spark gap D. The accumulated electric energy in 
the condenser then surges violently backwardsjand forwards, 



Fig. 34.—Wireless “Coupled” Transmitter. 


and by induction corresponding surgings are produced in 
the aerial circuit, these latter surgings setting up electric 
waves in the ether. 

For the sake of simplicity we have represented the 
apparatus as using an induction coil, but in all stations of 
any size the coil is replaced by a step-up transformer, and 

187 































Electricity 

the current is supplied either from an electric light power 
station at some town near by, or from a power house specially 
built for the purpose. Alternating current is generally used, 
and if the current supplied is continuous, it is converted into 
alternating current. This may be done by making the 
continuous current drive an electric motor, which in turn 
drives a dynamo generating alternating current. In any 
case, the original current is too low in voltage to be used 
directly, but in passing through the transformer it is raised 
to the required high pressure. The transmitting key, 
which is inserted between the dynamo and the transformer, 
is specially constructed to prevent the operator from receiv¬ 
ing accidental shocks, and the spark gap is enclosed in a 
sort of sound-proof box, to deaden the miniature thunders 
of the discharge. 

During the time that signals are being transmitted, 
sparks follow one another across the spark gap in rapid 
succession, a thousand sparks per second being by no 
means an uncommon rate. The violence of these rapid 
discharges raises the brass balls of the gap to a great heat. 
This has the effect of making the sparking spasmodic and 
uncertain, with the result that the signals at the receiving 
station are unsatisfactory. To get over this difficulty 
Marconi introduced a rotary spark gap. This is a wheel 
with projecting knobs or studs, mounted on the shaft of the 
dynamo supplying the current, so that it rotates rapidly. 
Two stationary knobs are fixed so that the wheel rotates 
between them, and the sparks are produced between these 
fixed knobs and those of the wheel, a double spark gap 
thus being formed. Overheating is prevented by the 
currents of air set up by the rapid movement of the wheel, 
and the sparking is always regular. 

In the receiving apparatus already described a filings 
coherer was used to detect the ether waves, and, by means 

188 


PLATE XIII. 



Photo by 


Daily Mirror. 


(a) MARCONI OPERATOR RECEIVING A MESSAGE. 



By permission of The Marconi Co. Ltd. 

( b ) MARCONI MAGNETIC DETECTOR. 




















Wireless Telegraphy and Telephony 

of a local battery, to translate them into audible signals with 
a sounder, or printed signals with a Morse inker. This 
coherer however is unsuitable for commercial working. 
It is not sufficiently sensitive, and it can be used only for 
comparatively short distances ; while its action is so slow 
that the maximum speed of signalling is not more than 
about seventeen or eighteen words a minute. A number 
of different detectors of much greater speed and sensitive¬ 
ness have been devised. The most reliable of these, 
though not the most sensitive, is the Marconi magnetic de¬ 
tector, Plate XI11. b. This consists of a moving band made 
of several soft iron wires twisted together, and passing close 
to the poles of two horse-shoe magnets. As the band 
passes from the influence of one magnet to that of the other 
its magnetism becomes reversed, but the change takes a 
certain amount of time to complete owing to the fact that 
the iron has some magnetic retaining power, so that it 
resists slightly the efforts of one magnet to reverse the 
effect of the other. The moving band passes through two 
small coils of wire, one connected with the aerial, and the 
other with a specially sensitive telephone receiver. When 
the electric waves from the transmitting station fall upon 
the aerial of the receiving station, small, rapidly oscillating 
currents pass through the first coil, and these have the 
effect of making the band reverse its magnetism instantly. 
The sudden moving of the lines of magnetic force induces 
a current in the second coil, and produces a click in the 
telephone. As long as the waves continue, the clicks 
follow one another rapidly, and they are broken up into the 
long and short signals of the Morse code according to the 
manipulation of the Morse key at the sending station. 
Except for winding up at intervals the clockwork mechanism 
which drives the moving band, this detector requires no 
attention, and it is always ready for work. 

189 


Electricity 

Another form of detector makes use of the peculiar 
power possessed by certain crystals to rectify the oscillatory 
currents received from the aerial, converting them into 
uni-directional currents. At every discharge of the con¬ 
denser at the sending station a number of complete waves, 
forming what is called a “ train ” of waves, is set in motion. 
From each train of waves the crystal detector produces one 
uni-directional pulsation of current, and this causes a click 
in the telephone receiver. If these single pulsations follow 
one another rapidly and regularly, a musical note is heard 
in the receiver. Various combinations of crystals, and 
crystals and metal points, are used, but all work in the 
same way. Some combinations work without assistance, 
but others require to have a small current passed through 
them from a local battery. The crystals are held in small 
cups of brass or copper, mounted so that they can be 
adjusted by means of set-screws. Crystal detectors are 
extremely sensitive, but they require very accurate adjust¬ 
ment, and any vibration quickly throws them out of order. 

The “electrolytic” detector rectifies the oscillating 
currents in a different manner. One form consists of a thin 
platinum wire passing down into a vessel made of lead, 
and containing a weak solution of sulphuric acid. The 
two terminals of a battery are connected to the wire and 
the vessel respectively. As long as no oscillations are 
received from the aerial the current is unable to flow 
between the wire and the vessel, but when the oscillations 
reach the detector the current at once passes, and operates 
the telephone receiver. The action of this detector is not 
thoroughly understood, and the way in which the point of 
the platinum wire prevents the passing of the current until 
the oscillations arrive from the aerial is something of a 
mystery. 

The last detector that need be described is the Fleming 

190 


Wireless Telegraphy and Telephony 

valve receiver. This consists of an electric incandescent 
lamp, with either carbon or tungsten filament, into which 
is sealed a plate of platinum connected with a terminal out¬ 
side the lamp. The plate and the filament do not touch 
one another, but when the lamp is lighted up a current can 
be passed from the plate to the filament, but not from fila¬ 
ment to plate. This receiver acts in a similar way to the 
crystal detector, making the oscillating currents into uni¬ 
directional currents. It has proved a great success for 
transatlantic wireless communication between the Marconi 
stations at Clifden and Glace Bay, and is extensively used. 

The electric waves set in motion by the transmitting 
apparatus of a wireless station spread outwards through 
the ether in all directions, and so instead of reaching only 
the aerial of the particular station with which it is desired 
to communicate, they affect the aerials of all stations within 
a certain range. So long as only one station is sending 
messages this causes no trouble ; but when, as is actually 
the case, large numbers of stations are hard at work trans¬ 
mitting different messages at the same time, it is evident 
that unless something can be done to prevent it, each of 
these messages will be received at the same moment by 
every station within range, thus producing a hopeless con¬ 
fusion of signals from which not a single message can be 
read. Fortunately this chaos can be avoided by what is 
called “ tuning.” 

Wireless tuning consists in adjusting the aerial of the 
receiving station so that it has the same natural rate of 
oscillation as that of the transmitting station. A simple 
experiment will make clearer the meaning of this. If we 
strike a tuning-fork, so that it sounds its note, and while it 
is sounding strongly place near it another fork of the same 
pitch and one of a different pitch, we find that the fork of 
similar pitch also begins to sound faintly, whereas the third 

191 


Electricity 

fork remains silent. The explanation is that the two forks 
of similar pitch have the same natural rate of vibration, 
while the other fork vibrates at a different rate. When 
the first fork is struck, it vibrates at a certain rate, and sets 
in motion air waves of a certain length. These waves 
reach both the other forks, but their effect is different in 
each case. On reaching the fork of similar pitch the first 
wave sets it vibrating, but not sufficiently to give out a 
sound. But following this wave come others, and as the 
fork has the same rate of vibration as the fork which 
produced the waves, each wave arrives just at the right 
moment to add its impulse to that of the preceding wave, 
so that the effect accumulates and the fork sounds. In the 
case of the third fork of different pitch, the first wave sets 
it also vibrating, but as this fork cannot vibrate at the same 
rate as the one producing the waves, the latter arrive at 
wrong intervals; and instead of adding together their 
impulses they interfere with one another, each upsetting 
the work of the one before it, and the fork does not sound. 
The same thing may be illustrated with a pendulum. If 
we give a pendulum a gentle push at intervals correspond¬ 
ing to its natural rate of swing, the effects of all these 
pushes are added together, and the pendulum is made to 
swing vigorously. If, on the other hand, we give the pushes 
at longer or shorter intervals, they will not correspond with 
the pendulum’s rate of swing, so that while some pushes 
will help the pendulum, others will hinder it, and the final 
result will be that the pendulum is brought almost to a 
standstill, instead of being made to swing strongly and 
regularly. The same principle holds good with wireless 
aerials. Any aerial will respond readily to all other aerials 
having the same rate of oscillation, because the waves in 
each case are of the same length ; that is to say, they follow 
one another at the same intervals. On the other hand, an 


Wireless Telegraphy and Telephony 

aerial will not respond readily to waves from another aerial 
having a different rate of oscillation, because these do not 
follow each other at intervals to suit it. 

If each station could receive signals only from stations 
having aerials similar to its own, its usefulness would be 
very limited, and so all stations are provided with means 
of altering the rate of oscillation of their aerials. The 
actual tuning apparatus by which this is accomplished need 
not be described, as it is complicated, but what happens in 
practice is this : The operator, wearing telephone receivers 
fixed over his ears by means of a head band, sits at a 
desk upon which are placed his various instruments. He 
adjusts the tuning apparatus to a position in which 
signals from stations of widely different wave-lengths are 
received fairly well, and keeps a general look out over 
passing signals. Presently he hears his own call-signal, 
and knows that some station wishes to communicate with 
him. Immediately he alters the adjustment of his tuner 
until his aerial responds freely to the waves from this 
station, but not to waves from other stations, and in this 
way he is able to cut out signals from other stations and to 
listen to the message without interruption. 

Unfortunately wireless tuning is yet far from perfect in 
certain respects. For instance, if two stations are trans¬ 
mitting at the same time on the same wave-length, it is 
clearly impossible for a receiving operator to cut one out 
by wave-tuning, and to listen to the other only. In such 
a case, however, it generally happens that although the 
wave-frequency is the same, the frequency of the wave 
groups or trains is different, so that there is a difference 
in the notes heard in the telephones; and a skilful operator 
can distinguish between the two sufficiently well to read 
whichever message is intended for him. The stations 
which produce a clear, medium-pitched note are the easiest 
n 193 


Electricity 

to receive from, and in many cases it is possible to identify 
a station at once by its characteristic note. Tuning is also 
unable to prevent signals from a powerful station close at 
hand from swamping to some extent signals from another 
station at a great distance, the nearer station making the 
receiving aerial respond to it as it were by brute force, 
tuning or no tuning. 

Another source of trouble lies in interference by atmo¬ 
spheric electricity. Thunderstorms, especially in the 
tropics, interfere greatly with the reception of signals, 
the lightning discharges giving rise to violent, irregular 
groups of waves which produce loud noises in the tele¬ 
phones. There are also silent electrical disturbances in the 
atmosphere, and these too produce less strong but equally 
weird effects. Atmospheric discharges are very irregular, 
without any real wave-length, so that an operator cannot 
cut them out by wave-tuning pure and simple in the way 
just described, as they defy him by affecting equally all 
adjustments. Fortunately, the irregularity of the atmo¬ 
spherics produces correspondingly irregular sounds in the 
telephones, quite unlike the clear steady note of a wireless 
station ; and unless the atmospherics are unusually strong 
this note pierces through them, so that the signals can be 
read. The effects of lightning discharges are too violent 
to be got rid of satisfactorily, and practically all that can 
be done is to reduce the loudness of the noises in the 
telephones, so that the operator is not temporarily deafened. 
During violent storms in the near neighbourhood of a 
station it is usual to connect the aerial directly to earth, 
so that in the event of its being struck by a flash the 
electricity passes harmlessly away, instead of injuring the 
instruments, and possibly also the operators. Marconi 
stations are always fitted with lightning-arresters. 

The methods and apparatus we have described so far 

194 


Wireless Telegraphy and Telephony 

are those of the Marconi system, and although in practice 
additional complicated and delicate pieces of apparatus are 
used, the description given represents the main features of 
the system. Although Marconi was not the discoverer of 
the principles of wireless telegraphy, he was the first to 
produce a practical working system. In 1896 Marconi came 
from Italy to England, bringing with him his apparatus, 
and after a number of successful demonstrations of its 
working, he succeeded in convincing even the most scep¬ 
tical experts that his system was thoroughly sound. Com¬ 
mencing with a distance of about 100 yards, Marconi 
rapidly increased the range of his experiments, and by 
the end of 1897 he succeeded in transmitting signals 
from Alum Bay, in the Isle of Wight, to a steamer 18 
miles away. In 1899 messages were exchanged between 
British warships 85 miles apart, and the crowning achieve¬ 
ment was reached in 1901, when Marconi received readable 
signals at St. John’s, Newfoundland, from Poldhu in Corn¬ 
wall, a distance of about 1800 miles. In 1907 the Marconi 
stations at Clifden and Glace Bay were opened for public 
service, and by the following year transatlantic wireless 
communication was in full swing. The sending of wireless 
signals across the Atlantic was a remarkable accomplish¬ 
ment, but it did not represent by any means the limits 
of the system, as was shown in 1910. In that year 
Marconi sailed for Buenos Ayres, and wireless communica¬ 
tion with Clifden was maintained up to the almost incredible 
distance of 4000 miles by day, and 6735 miles by night. 
The Marconi system has had many formidable rivals, but 
it still holds the proud position of the most successful com¬ 
mercial wireless system in the world. 

We have not space to give a description of the other 
commercial systems, but a few words on some of the chief 
points in which they differ from the Marconi system may 

195 


Electricity 

be of interest. We have seen that an ordinary spark gap, 
formed by two metal balls a short distance apart, becomes 
overheated by the rapid succession of discharges, with the 
result that the sparking is irregular. What actually 
happens is that the violent discharge tears off and vapor¬ 
izes minute particles of the metal. This intensely heated 
vapour forms a conducting path which the current is able 
to cross, so that an arc is produced just in the same way 
as in the arc lamp. This arc is liable to be formed by 
each discharge, and it lasts long enough to prevent the 
sparks from following one another promptly. In the 
Marconi system this trouble is avoided by means of a 
rotating spark gap, but in the German “Telefunken” 
system, so named from Greek tele , far off, and German 
Funke , a spark, a fixed compound spark gap is used 
for the same purpose. This consists of a row of metal 
discs about inch apart, and the spark leaps these 

tiny gaps one after the other. The discs are about 
3 inches in diameter, and their effect is to conduct away 
quickly the heat of the discharge. By this means the 
formation of an arc is prevented, and the effect of each 
discharge is over immediately, the sparks being said to be 
“quenched.” The short discharges enable more energy to 
be radiated from the aerial into the ether, and very high 
rates of sparking are obtained, producing a high-pitched 
musical note. 

The “ Lepel ” system also uses a quenched spark. 
The gap consists of two metal discs clamped together and 
separated only by a sheet of paper. The paper has a hole 
through its centre, and through this hole the discharge 
takes place, the discs being kept cool by water in constant 
circulation. The discharge is much less noisy than in the 
Marconi and Telefunken systems, and the musical note 
produced is so sensitive that by varying the adjustments 

196 



Wireless Telegraphy and Telephony 

simple tunes can be played, and these can be heard quite 
distinctly in the telephone at the receiving stations. 

In the three systems already mentioned spark 
discharges are used to set up oscillatory currents in the 
aerial, which in turn set up waves in the ether. Each 
discharge sets in motion a certain number of waves, 
forming what is known as a train of waves. The dis¬ 
charges follow one another very rapidly, but still there is a 
minute interval between them, and consequently there is a 
corresponding interval between the wave-trains. In the 
“ Goldschmidt ” system the waves are not sent out in 
groups of this kind, but in one long continuous stream. 
The oscillatory currents which produce ether waves are 
really alternating currents which flow backwards and 
forwards at an enormous speed. The alternating current 
produced at an ordinary power station is of no use for 
wireless purposes, because its “frequency,” or rate of flow 
backwards and forwards, is far too low. It has been 
found possible however to construct special dynamos 
capable of producing alternating current of the necessary 
high frequency, and such dynamos are used in the 
Goldschmidt system. The dynamos are connected directly 
to the aerial, so that the oscillatory currents in the latter 
are continuous, and the ether waves produced are con¬ 
tinuous also. 

The “ Poulsen ” system produces continuous waves in 
an altogether different manner, by means of the electric 
arc. The arc is formed between a fixed copper electrode 
and a carbon electrode kept in constant rotation, and it is 
enclosed in a kind of box filled with methylated spirit 
vapour, hydrogen, or coal gas. A powerful electro-magnet 
is placed close to the arc, so that the latter is surrounded 
by a strong magnetic field. Connected with the terminals 
of the arc is a circuit consisting of a condenser and a coil 

197 


Electricity 

of wire, and the arc sets up in this circuit oscillatory 
currents which are communicated to the aerial. These 
currents are continuous, and so also are the resulting 
waves. 

The method of signalling employed in these two 
continuous-wave systems is quite different from that used 
in the Marconi and other spark systems. It is practically 
impossible to signal by starting and stopping the alternating- 
current dynamos or the arc at long or short intervals to 
represent dashes or dots. In one case the sudden changes 
from full load to zero would cause the dynamo to vary its 
speed, and consequently the wave - length would be 
irregular; besides which the dynamo would be injured by 
the sudden strains. In the other case it would be 
extremely difficult to persuade the arc to start promptly 
each time. On this account the dynamo and the arc are 
kept going continuously while a message is being trans¬ 
mitted, and the signals are given by altering the wave¬ 
length. In other words, the transmitting aerial is thrown 
in and out of tune alternately at the required long or short 
intervals, and the receiving aerial responds only during the 
“ in-tune ” intervals. 

The various receiving detectors previously described 
are arranged to work with dis-continuous waves, producing 
a separate current impulse from each group or train of 
waves. In continuous wave systems there are of course 
no separate groups, and for this reason these detectors are 
of no use, and a different arrangement is required. The 
oscillatory currents set up in the aerial are allowed to 
charge up a condenser, and this condenser is automatically 
disconnected from the aerial and connected to the operators 
telephones at regular intervals of about roW second. 
Each time the condenser is connected to the telephones 
it is discharged, and a click is produced. These clicks 

198 



Wireless Telegraphy and Telephony 

continue only as long as the waves are striking the aerial, 
and as the transmitting operator interrupts the waves at 
long or short intervals the clicks are split up into groups of 
corresponding length. 

Continuous waves have certain advantages over dis¬ 
continuous waves, particularly in the matter of sharp 
tuning, but these advantages are outweighed to a large 
extent by weak points in the transmitting apparatus. The 
dynamos used to produce the high-frequency currents in 
the Goldschmidt system are very expensive to construct 
and troublesome to keep in order; while in the Poulsen 
system the arc is difficult to keep going for long periods, 
and it is liable to fluctuations which greatly affect its 
working power. Although all the commercial Marconi 
installations make use of dis-continuous waves exclusively, 
Mr. Marconi is still carrying out experiments with con¬ 
tinuous waves. 

There are many points in wireless telegraphy yet to be 
explained satisfactorily. Our knowledge of the electric 
ether waves is still limited, and we do not know for certain 
how these waves travel from place to place, or exactly 
what happens to them on their journeys. For this reason 
we are unable to give a satisfactory explanation of the 
curious fact that, generally speaking, it is easier to signal 
over long distances at night than during the day. Still 
more peculiar is the fact that it is easier to signal in a 
north and south direction than in an east and west 
direction. There are also remarkable variations in the 
strength of the signals at certain times, particularly about 
sunset and sunrise. Every station has a certain normal 
range which does not vary much as a rule, but at odd 
times astonishing “freak” distances are covered, stations 
having for a short time ranges far beyond their usual limits. 
These and other problems are being attacked by many 

199 


Electricity 

investigators, and no doubt before very long they will be 
solved. Wireless telegraphy already has reached remark¬ 
able perfection, but it is still a young science, and we may 
confidently expect developments which will enable us to 
send messages with all speed across vast gulfs of distance 
at present unconquered. 

Wireless telephony, like wireless telegraphy, makes use 
of electric waves set up in, and transmitted through the 
ether. The apparatus is practically the same in each case, 
except in one or two important points. In wireless 
telegraphy either continuous or dis-continuous waves may 
be used, and in the latter case the spark-frequency may be 
as low as twenty-five per second. On the other hand, 
wireless telephony requires waves which are either 
continuous, or if dis-continuous, produced by a spark- 
frequency of not less than 20,000 per second. In other 
words, the frequency of the wave trains must be well above 
the limits of audibility. Although dis-continuous waves of 
a frequency of from 20,000 to 40,000 or more per second 
can be used, it has been found more convenient to use 
absolutely continuous waves for wireless telephony, and 
these may be produced by the Marconi disc generator, by 
the Goldschmidt alternator, or by the Poulsen arc, the last 
named being largely employed. 

In wireless telegraphy the wave trains are split up by 
a transmitting key so as to form groups of signals ; but in 
telephony the waves are not interrupted at all, but are 
simply varied in intensity by means of the voice. All 
telephony, wireless or otherwise, depends upon the pro¬ 
duction of variations in the strength of a current of 
electricity, these variations being produced by air vibrations 
set up in speaking. In ordinary telephony with connecting 
wires the current variations are produced by means of a 
microphone in the transmitter, and in wireless telephony 

200 


Wireless Telegraphy and Telephony 

the same principle is adopted. Here comes in the out¬ 
standing difficulty in wireless transmission of speech. The 
currents used in ordinary telephony are small, and the 
microphone works with them quite satisfactorily ; but in 
wireless telephony very heavy currents have to be em¬ 
ployed, and so far no microphone has proved capable of 
dealing effectively with these currents. Countless devices 
to assist the microphone have been tried. It was found 
that one of the causes of trouble was the overheating of 
the carbon granules, which caused them to stick together, 
so becoming insensitive. To remedy this the granules 
have been cooled in various ways, by water, gas, or oil, but 
although the results have been improved, still the micro¬ 
phones worked far from perfectly. Improved results 
have been obtained also by connecting a number of 
microphones in parallel. The microphone difficulty is 
holding back the development of wireless telephony, and 
at present no satisfactory solution of the problem is in 
sight. 

The transmitting and receiving aerials are the same as 
in wireless telegraphy, and like them are tuned to the same 
frequency. The receiving apparatus too is of the ordinary 
wireless type, with telephones and electrolytic or other 
detectors. 

Wireless telephony has been used with considerable 
success in various German collieries, and at the Dinnington 
Main Colliery, Yorkshire. Early last year Marconi suc¬ 
ceeded in establishing communication by wireless telephony 
between Bournemouth and Chelmsford, which are about 
ioo miles apart; and about the same time a song sung 
at Laeken, in Belgium, was heard clearly at the Eiffel 
Tower, Paris, a distance of 225 miles. The German 
Telefunken Company have communicated by wireless 
telephony between Berlin and Vienna, 375 miles, and 

201 




Electricity 

speech has been transmitted from Rome to Tripoli, a total 
distance of more than 600 miles. These distances are of 
course comparatively small, but if the microphone trouble 
can be overcome satisfactorily, transatlantic wireless 
telephony appears to be quite possible. 


202 


CHAPTER XXI 


WIRELESS TELEGRAPHY—PRACTICAL 

APPLICATIONS 

A fairly good idea of the principles and apparatus of wire¬ 
less telegraphy should have been gained in reading Chapter 
XX., but so far little has been said about its practical use. 
If we leave their power out of consideration, wireless 
stations may be divided into two classes : fixed stations on 
land, and moving stations, if the expression may be allowed, 
on ships. For moving stations wireless telegraphy has 
the field all to itself, but for communication between fixed 
stations it comes into conflict with ordinary telegraphy by 
wire or cable. As regards land messages over compara¬ 
tively short distances, say throughout Great Britain, wireless 
telegraphy has no advantages over the older methods; and 
it is extremely unlikely that it ever will be substituted 
for the existing cable telegraphy. For long distances 
overland wireless has the great advantage of having all its 
apparatus concentrated at two points. A long land line 
passing through wild country, and exposed to all kinds of 
weather, requires constant labour to keep it in good repair, 
and when a breakdown occurs at any point, the repairing 
gang may be miles away, so that delay is caused. On the 
other hand, whatever may go wrong at a wireless station, 
no time is lost in effecting the necessary repairs, for every¬ 
thing is on the spot. 

At present there is no great competition between wire- 

203 


Electricity 

less and ordinary telegraphy for overland messages of any 
kind, but the case is different when we come to communication 
across seas and oceans. Already the cable companies have 
been affected considerably, and there is little doubt that 
they will feel the competition much more seriously before 
long. The general public, always conservative in such 
matters, have not yet grasped the fact that telegrams can 
be handed in at any telegraph office in the British Isles, 
and at most telegraph offices in the United States and 
Canada, for wireless transmission across the Atlantic, via 
the Marconi stations at Clifden and Glace Bay. The cost 
is remarkably small, being eightpence a word for ordinary 
messages. 

It is impossible to state with any accuracy how many 
land wireless stations there are in the world, but the list 
given in the Year-Book of Wireless Telegraphy for 1915 
enumerates about 700 stations. This list does not include 
private or experimental stations, and also many stations 
used exclusively for naval or military purposes are not 
given. The information available about these 700 stations 
is incomplete in many cases, but about 500 are controlled 
by various departments of the governments of the different 
states. Of the remainder, about 100 are controlled by the 
Marconi Company, the rest being in the hands of various 
wireless, commercial, or railway companies. 

Amongst the most important land stations are the 
Clifden and Glace Bay transatlantic stations. They are 
very similar in plan, and each has a separate aerial for 
sending and for receiving. Contrary to the usual practice, 
continuous current is used to charge the condensers. In 
Chapter IV. we saw how a current of high voltage could 
be obtained by connecting a number of cells in series, and 
at these stations the necessary high voltage is produced by 
connecting a number of powerful dynamos in series, on the 

204 


Wireless Telegraphy 

same principle. Along with the dynamos a huge battery 
of accumulators, consisting of about 6000 cells, is used as 
a sort of reservoir of current. These stations have a 
normal range of considerably over 3000 miles. Last year 
a large transmitting station was completed at Cefndu, near 
Carnarvon. This station, which is probably the most 
powerful in existence, is intended to communicate directly 
with New Jersey, United States, as an alternative to the 
Clifden-Glace Bay route. 

Other powerful stations are Poldhu, in Cornwall, of 
which we shall speak later; the French Eiffel Tower 
station ; the German station at Nauen, near Berlin, which 
last year succeeded in exchanging messages with Windhoek, 
German South-West Africa, a distance of nearly 6000 
miles ; and the extremely powerful station at Coltano, Italy. 
France has three stations in West Africa with a night 
range of 1600 miles; and Italy one in Somaliland with a 
normal range of about the same distance. The recently 
opened Chinese stations at Canton, Foochow, and Woosung 
have a range of 1300 miles by night, and 650 miles by day. 
With the fall of Tsingtau, China, Germany lost a wireless 
station capable of signalling over 1350 miles at night. 
Japan has six stations with a night range of over 1000 
miles. Massawa, on the Red Sea, has a range of 1600 
miles, and New Zealand has two stations with ranges of 
1200 miles by day, and 2500 miles by night. Australia 
has a large number of stations with a normal range of 
about 500 miles. In the United States, which has a very 
large number of stations, Arlington, Virginia, covers 1000 
miles, and Sayville from 600 to 2300 miles. South 
America has not many high-power stations, but Cerrito, in 
Uruguay, has a range of about 1000 miles. 

Until a thoroughly practical system of long-distance 
wireless telephony is developed, wireless telegraphy will 

205 


Electricity 

remain the only possible means of communication between 
ships and shore, or between one ship and another, except 
where the distance is so small that some method of sema¬ 
phore signalling can be used. In the days when wireless 
was unknown, a navigator was thrown entirely upon his 
own resources as soon as his vessel was out of sight of 
land, for no information of any kind could reach him. 
Even with a wireless installation on board, the captain of a 
vessel still needs the same skill and watchfulness as of old, 
but in the times of uncertainty and danger to which all 
ships are liable, he often is able to obtain information which 
may prevent disaster. In order to determine accurately 
his position, a navigator requires to know the exact Green¬ 
wich Mean Time, and he gets this time from his chrono¬ 
meters. These are wonderfully reliable instruments, but 
even they may err at times. To avoid the possibility of 
mistakes from this cause, wireless time signals are sent out 
at regular intervals by certain high-power stations, and as 
long as a vessel is within range of one of these stations the 
slightest variation in the chronometers may be detected 
immediately. Amongst these stations are the Eiffel Tower, 
giving time signals at io a.m. and at midnight; and Nord- 
deich, Germany, giving signals at noon and midnight. 
These time signals have proved most useful also on land, 
more particularly for astronomers and for explorers engaged 
on surveying work. 

In addition to time signals, other valuable information 
is conveyed by wireless to ships at sea. A ship encounter¬ 
ing ice, or a derelict, reports its discovery to other ships 
and to the shore stations, and in this way vessels coming 
along the same route are warned of the danger in time to 
take the necessary precautions. Weather reports are issued 
regularly from various shore stations in most parts of the 
world. The completeness of the information given varies 

206 


Wireless Telegraphy 

a good deal with different stations, but in many cases it 
includes a report of the existing state of the weather at a 
number of different places, a forecast of the winds likely 
to be encountered at sea, say at a distance of ioo miles 
from land, and warnings of approaching storms, with 
remarks on any special atmospheric conditions at the time 
of sending. In Europe weather reports are issued daily 
from the Admiralty station at Cleethorpes, the Eiffel Tower, 
and Norddeich; and in the United States more than a 
dozen powerful stations are engaged in this work. 

Another valuable use of wireless is in carrying on the 
work of lighthouses and lightships during snowstorms or 
dense fogs, which the light cannot penetrate. So far not 
much has been done in this direction, but the French 
Government have decided to establish wireless lighthouses 
on the islands outside the port of Brest, and also at Havre. 
Automatic transmitting apparatus will be used, sending 
out signals every few seconds, and working for periods of 
about thirty hours without attention. 

The improvement in the conditions of ocean travel 
wrought by wireless telegraphy is very remarkable. The 
days when a vessel, on passing out of sight of land, entered 
upon a period of utter isolation, is gone for ever. Unless 
it strays far from all recognized trade routes, a ship fitted 
with a wireless installation is never isolated ; and with the 
rapidly increasing number of high-power stations both on 
land and sea, it soon will be almost impossible for a vessel 
to find a stretch of ocean beyond the reach of wave-borne 
messages. The North Atlantic Ocean is specially remark¬ 
able for perfection of wireless communication. For the 
first 250 miles or so after leaving British shores, liners are 
within reach of various coast stations, and beyond this 
Poldhu takes up the work and maintains communication 
up to about mid-Atlantic. On passing beyond the reach 

207 


Electricity 

of Poldhu, liners come within range of other Marconi 
stations at Cape Cod, Massachusetts, and Cape Race, 
Newfoundland, so that absolutely uninterrupted communi¬ 
cation is maintained throughout the voyage. On many 
liners a small newspaper is published daily, in which are 
given brief accounts of the most striking events of the 
previous day, together with Stock Exchange quotations and 
market prices. This press news is sent out during the 
night from Poldhu and Cape Cod. During the whole 
voyage messages may be transmitted from ship to shore, 
or from shore to ship, with no more difficulty, as far as the 
public are concerned, than in sending an ordinary inland 
telegram. 

The transmitting ranges of ship installations vary 
greatly, the range of the average ocean liner being about 
250 miles. Small ships come as low as 50 miles, while a 
few exceptional vessels have night ranges up to 1200 or 
even 2500 miles. Although an outward-bound vessel is 
almost always within range of some high-power shore 
station, it is evident that it soon must reach a point beyond 
which it is unable to communicate directly with the shore. 
This difficulty is overcome by a system of relaying from 
ship to ship. The vessel wishing to speak with the shore 
hands on its message to some other vessel nearer to land 
or with a longer range, and this ship sends forward the 
message to a shore station if one is within its reach, and if 
not to a third vessel, which completes the transmission. 

The necessity for wireless installations on all sea-going 
vessels has been brought home to us in startling fashion on 
several occasions during the last few years. Time after 
time we have read thrilling accounts of ocean disasters in 
which wireless has come to the rescue in the most wonder¬ 
ful way. A magnificent liner, with its precious human 
freight, steams majestically out of harbour, and ploughs its 

208 


Wireless Telegraphy 

way out into the waste of waters. In mid-ocean comes 
disaster, swift and awful, and the lives of all on board are 
in deadly peril. Agonized eyes sweep the horizon, but no 
sail is in sight, and succour seems hopeless. But on the 
deck of that vessel is a small, unpretentious cabin, and at a 
desk in that cabin sits a young fellow with strange-looking 
instruments before him. At the first tidings of disaster he 
presses a key, and out across the waters speed electric 
waves bearing the wireless cry for help, “S.O.S.,” in¬ 
cessantly repeated. Far away, on another liner, is a 
similar small cabin, and its occupant is busy with messages 
of everyday matters. Suddenly, in the midst of his work, 
comes the call from the stricken vessel, and instantly all 
else is forgotten. No matter what the message in hand, it 
must wait, for lives are in danger. Quickly the call is 
answered, the position of the doomed ship received, and 
the captain is informed. A few orders are hurriedly given, 
the ship’s course is changed, and away she steams to the 
rescue, urged on by the full power of her engines. In an 
hour or two she arrives alongside, boats are lowered, and 
passengers and crew are snatched from death and placed 
in safety. This scene, with variations, has been enacted 
many times, and never yet has wireless failed to play its 
part. It is only too true that in some instances many 
lives have been lost, but in these cases it is necessary to 
remember that without wireless every soul on board might 
have gone down. The total number of lives already saved 
by wireless is estimated at about 5000, and of these some 
3000 have been saved in the Atlantic. 

Ship aerials are carried from one mast to another, as 
high up as possible. The transmitting and receiving 
apparatus is much the same as in land stations, so that it 
need not be described. In addition, most liners carry a 
large induction coil and a suitable battery, so that distress 
o 209 


Electricity 

signals can be transmitted even when the ordinary 
apparatus is rendered useless by the failure of the current 
supply. Most of the wireless systems are represented 
amongst ship installations, but the great majority of vessels 
have either Marconi or Telefunken apparatus. 

Every wireless station, whether on ship or on shore, has 
a separate call-signal, consisting of three letters. For 
instance, Clifden is MFT, PoldhuMPD, Norddeich KAV, 
s.s. Lusitania MFA, and H.M.S. Dreadnought BAU. 
Glace Bay, GB, and the Eiffel Tower, P'L, have two 
letters only. In order to avoid confusion, different countries 
have different combinations of letters assigned to them 
exclusively, and these are allotted to the various ship 
and shore stations. For example, Great Britain has all 
combinations beginning with B, G, and M; France all 
combinations beginning with F, and also the combinations 
UAA to UMZ ; while the United States is entitled to use 
all combinations beginning with N and W, and the com¬ 
binations KIA to KZZ. There are also special signals to 
indicate nationality, for use by ships, British being indicated 
by-, Japanese by-, and so on. 

Wireless telegraphy apparently has a useful future in 
railway work. In spite of the great perfection of present- 
day railway signalling, no railway company is able to avoid 
occasional accidents. Some of these accidents are due to 
circumstances which no precautions can guard against 
entirely, such, for instance, as the sudden breakage of some 
portion of the mechanism of the train itself. In many cases, 
however, the accident is caused by some oversight on the 
part of the signalman or the engine-driver. Probably the 
great majority of such accidents are not due to real care¬ 
lessness or inattention to duty, but to unaccountable freaks 
of the brain, through which some little detail, never before 
forgotten, is overlooked completely until too late. We all 

210 





Wireless Telegraphy 

are liable to these curious mental lapses, but happily in most 
cases these do not lead to disaster of any kind. The ever¬ 
present possibility of accidents brought about in this way is 
recognized fully by railway authorities, and every effort is 
made to devise mechanism which will safeguard a train in 
case of failure of the human element. The great weakness 
of the ordinary railway system is that there is no reliable 
means of communicating with the driver of a train except 
by the fixed signals, so that when a train has passed one 
set of signals it is generally beyond the reach of a message 
until it arrives at the next set. On the enterprising 
Lackawanna Railroad, in the United States, an attempt has 
been made to remove this defect by means of wireless 
telegraphy, and the experiment has been remarkably 
successful. Wireless communication between moving 
passenger trains and certain stations along the route has 
been established, and the system is being rapidly developed. 

The wireless equipment of the stations is of the usual 
type, and does not call for comment, but the apparatus on 
the trains is worth mention. The aerial, which must be 
low on account of bridges and tunnels, consists of rectangles 
of wire fixed at a height of 18 inches above the roof of 
each car. These separate aerials are connected together 
by a wire running to a small operating room containing a 
set of Marconi apparatus, and situated at the end of one of 
the cars. The earth connexion is made to the track rails, 
and the current is taken from the dynamos used to supply 
the train with electric light. With this equipment messages 
have been transmitted and received while the train was 
running at the rate of 70 miles an hour, and distances 
up to 125 miles have been covered. During a severe 
storm in the early part of last year the telegraph and 
telephone lines along the railroad broke down, but 
uninterrupted communication was maintained by wireless, 

211 


Electricity 

and the operations of the relief gangs and the snow-ploughs 
were directed by this means. For emergency signalling 
this system is likely to prove of enormous importance. If 
signals are set wrongly, through some misunderstanding, 
and a train which should have been held up is passed 
forward into danger, it can be stopped by a wireless message 
in time to prevent an accident. Again, if a train has a 
breakdown, or if it sticks fast in a snow-drift, its plight and 
its exact position can be signalled to the nearest station, so 
that help may be sent without delay. The possibilities of 
the system in fact are almost unlimited, and it seems not 
unlikely that wireless telegraphy will revolutionize the 
long-distance railway travelling of the future. 


212 


CHAPTER XXII 


ELECTROPLATING AND ELECTROTYPING 

In our chapter on the accumulator or storage cell we saw 
that a current of electricity has the power of decomposing 
certain liquids ; that is to say, it is able to split them up 
into their component parts. This power has given rise 
to the important art of electroplating and electrotyping. 
Electroplating is the process of depositing a coating of a 
rarer metal, such as gold, silver, or nickel, upon the 
surface of baser or commoner metals ; and electrotyping is 
the copying of casts, medals, types, and other similar 
objects. The fact that metals could be deposited by the 
decomposition of a solution by a current was known in the 
early days of the voltaic cell, but no one seems to have 
paid much attention to it. An Italian chemist published 
in 1805 an account of his success in coating two silver 
medals with gold, and some thirty years later Bessemer 
transformed lead castings into fairly presentable ornaments 
by coating them with copper, but commercial electro¬ 
plating may be said to have begun about 1840, when an 
Englishman named Elkington took out a patent for the 
process. Since then the processes of electroplating and 
electrotyping have rapidly come more and more into use, 
until to-day they are practised on a vast scale, giving em¬ 
ployment to thousands. 

Electroplating on a small scale is a very simple affair. 
A solution of the metal which it is desired to deposit is 

213 


Electricity 

placed in a suitable vessel. Two metal rods are placed 
across the top of this vessel, and from one of these is 
suspended a plate of the same metal as that in the solution, 
and from the other is hung the article to receive the 
coating. The positive terminal of a voltaic battery is 
connected to the rod supporting the plate, and the negative 
terminal to the rod carrying the article to be plated. As 
the current passes through the solution from the plate to the 
article the solution is decomposed, and the article receives 
a coating of metal. The solution through which the 
current passes, and which is decomposed, is called the 
electrolyte , and the terminal points at which the current 
enters and leaves the solution are called electrodes. The 
electrode by which the current enters the electrolyte is 
called the anode , and the one by which it leaves is called 
the cathode. 

If we wish to deposit a coating of copper on, say, an 
old spoon which has been dismissed from household service, 
a solution of sulphate of copper must be made up and 
placed in a glass or stoneware jar. Two little rods of 
brass, copper, or any other good conductor are placed 
across the jar, one at each side, and by means of hooks of 
wire a plate of copper is hung from one rod and the spoon 
from the other. The positive terminal of a battery of 
Daniell cells is then connected to the anode rod which 
supports the copper plate, and the negative terminal to 
the cathode rod carrying the spoon. The current now 
commences its task of splitting up the copper-sulphate 
solution into pure copper and sulphuric acid, and depositing 
this copper upon the spoon. The latter is very quickly 
covered with a sort of “blush” copper, and the coating 
grows thicker and thicker as long as the current is kept 
at work. If there were no copper plate forming the anode 
the process would soon come to a standstill, on account of 

214 


Electroplating and Electrotyping 

the copper in the electrolyte becoming used up ; but as it 
is the sulphuric acid separated out of the electrolyte takes 
copper from the plate and combines with it to form a 
further supply of copper sulphate. In this way the strength 
of the solution is kept up, and the copper anode becomes 
smaller and smaller as the coating on the spoon increases 
in thickness. It is not necessary that the anode should 
consist of absolutely pure copper, because any impurities 
will be precipitated to the bottom or mixed with the 
solution, nothing but quite pure copper being deposited on 



Fig. 35.—Small Electroplating Outfit. 


the spoon. At the same time if the copper anode is very 
impure the electrolyte quickly becomes foul, and has to be 
purified or replaced by new solution. 

To nickel-plate the spoon we should require a nickel 
plate for the anode and a nickel solution ; to silver-plate it, 
a silver anode and solution, and so on. Fig. 35 shows sc 
simple but effective arrangement for amateur electro¬ 
plating in a small way. 

Electroplating on a commercial scale is of course a 
much more elaborate process, but the principle remains 
exactly the same. Fig. 36 shows the general arrangement 
of a plating shop. It is obviously extremely important 

215 






















































Electricity 

that the deposit on a plated article should be durable, and 
to ensure that the coating will adhere firmly the article 
must be cleaned thoroughly before being plated. Cleanli¬ 
ness in the ordinary domestic sense is not sufficient, for 
the article must be chemically clean. Some idea of the 
care required in this respect may be gained from the fact 
that if the cleaned surface is touched with the hand before 
being plated, the coating will strip off the parts that have 
been touched. The surfaces are first cleaned mechanically, 
and then chemically by immersion in solutions of acids or 
alkalies, the cleaning process varying to some extent with 
different metals. There is also a very interesting process 
of cleaning by electricity. The article is placed in a vat 
fitted with anode and cathode rods, just as in an ordinary 
plating vat, and containing a solution of hydrate of potash 
and cyanide of potassium. The anode consists of a carbon 
plate, and the article is hung from the cathode rod. 
Sufficient current is passed through the solution to cause 
gas to be given off rapidly at the cathode, and as this gas 
rises to the surface it carries with it the grease and dirt 
from the article, in the form of a dirty scum. After a 
short time the article becomes oxidized and discoloured, 
and the current is then reversed, so that the article be¬ 
comes the anode, and the carbon plate the cathode. The 
current now removes the oxide from the surface of the 
article, which is left quite bright and chemically clean. 

When thoroughly cleaned the articles are ready to be 
placed in the plating vats. These vats are usually made 
of wood lined with chemically pure lead, or of iron lined 
with enamel or cement. Anode and cathode rods made 
of brass are placed across the vats, and from these the 
anodes of the various metals and the articles to be plated 
are hung by hooks of nickel or brass. Any number of 
rods may be used, according to the size of the vat, so long 

216 


ANODE BOD 


Electroplating and Electrotyping 



217 


Fig. 36.—General Arrangement of an Electroplating Shop. 



































































































































































































































































































































Electricity 

as the articles have an anode on each side. If three rods 
are used the articles are hung from the centre one, and the 
anodes from the outside ones. If a number of small 
articles are to be plated together they are often suspended 
in perforated metal trays. Small articles are also plated 
by placing them in a perforated barrel of wood, or wood 
and celluloid, which revolves in the solution. While the 
articles are being plated the revolving of the barrel makes 
them rub one against the other, so that they are brightly 
burnished. Dog chains, cycle chain links, button-hooks, 
and harness fittings are amongst the articles plated by 
means of the revolving barrel. 

The strength of current required for different kinds of 
plating varies considerably, and if the work is to be of the 
best quality it is very important that the current should be 
exactly right for the particular process in hand. In order 
to adjust it accurately variable resistances of German silver 
wire are provided for each vat, the current having to pass 
through the resistance before reaching the solution. The 
volume and the pressure of the current are measured by 
amperemeters and voltmeters attached to the resistance 
boards. If the intensity of the current is too great the 
articles are liable to be “burnt,” when the deposit is dark 
coloured and often useless. 

When exceptionally irregular surfaces have to be plated 
it is sometimes necessary to employ an anode of special 
shape, in order to keep as uniform a distance as possible 
between the electrodes. If this is not done, those parts of 
the surface nearest the anode get more than their share of 
the current, and so they receive a thicker deposit than the 
parts farther away. 

An interesting process is that known as “ parcel-plating,” 
by which decorative coatings of different coloured metals 
can be deposited on one article. For instance, if it is 

218 


Electroplating and Electrotyping 

desired to have gold flowers on a silver brooch, the parts 
which are not to be gilded are painted over with a non¬ 
conducting varnish. When this varnish is quite dry the 
brooch is placed in the gilding vat and the current sent 
through in the usual way. The gold is then deposited only 
on the parts unprotected by varnish, and after the gilding 
the varnish is easily removed by softening it in turpentine 
and brushing with a bristle brush. More elaborate 
combinations of different coloured metals can be made in 
the same way. 

Sugar basins, cream jugs, ornamental bowls, cigarette 
cases, and other articles are often gilded only on the inside. 
The article is filled with gold solution and connected to the 
cathode rod. A piece of gold wrapped in calico is attached 
to the anode rod, suspended in the solution inside the 
article, and moved about quickly until the deposit is of the 
required thickness. 

The time occupied in plating is greatly shortened by 
stirring or agitating the solutions. This sets up a good 
circulation of the liquid, and a continual supply of fresh 
solution is brought to the cathode. At the same time the 
resistance to the current is decreased, and more current 
may be used without fear of burning. Fig. 37 shows an 
arrangement for this purpose. The solution is agitated by 
compressed air, and at the same time the cathode rods are 
moved backwards and forwards. Plating solutions are 
also frequently heated in order to hasten the rate of 
deposition. 

When the plating process is complete, the articles are 
removed from the vat, thoroughly swilled in water, and 
dried. They are then ready for finishing by polishing and 
burnishing, or they may be given a sort of frosted surface. 
During the finishing processes the appearance of the articles 
changes considerably, the rather dead-looking surface 

219 


Electricity 

produced by the plating giving place to the bright lustre 
of the particular metal. 

It sometimes happens that an article which has been 



By permission of\ 

Fig. 37.—Method of agitating solution in 


[IV. Canning dr 3 Co. 

Plating Vat. 


plated and polished shows little defects here and there in 
the deposit. In such a case it is not necessary to re-plate 
the whole article, for the defects can be made good by a 

220 










































































































































Electroplating and Electrotyping 

process of “ doctoring.” A piece of the same metal as that 
forming the deposit is placed between two pieces of wood, 
and a wire fastened to one end of it. At the other end 
several thicknesses of flannel are wrapped round and 
securely tied. This strip, which forms a miniature anode, 
is connected to the anode rod of the plating vat, and the 
article is connected to the cathode rod. The flannel is 
saturated with the plating solution, and the strip is rubbed 
gently over the defective places until the deposit formed is 
as thick as that on the rest of the article. If the work is 
done carefully the “ doctored ” portions cannot be distin¬ 
guished from the rest of the surface. 

Electroplating may be employed to give ships’ plates 
a coating of copper to prevent barnacles from sticking to 
them. The work is done in sections by building up to the 
side of the vessel a sort of vat of which the plate to be 
coated forms one side. The plate is thus at the same time 
the cathode and part of the vat. 

So far we have spoken only of electroplating objects 
made of metal. If we tried to copperplate a plaster cast 
by simply suspending it as we did our spoon, we should 
get no result at all, because the plaster is a non-conductor. 
But if we sprinkle plumbago over the cast so as to give it 
a conducting surface, we can plate it quite well. Practically 
all materials can be electroplated, but if they are non¬ 
conductors they must be given a conducting surface in the 
way just described or by some similar means. Even 
flowers and insects may be plated, and by giving them first 
a coating of copper and then a coating of gold, delicately 
beautiful results are obtained. 

Electrotyping is practically the same as electroplating, 
except that the coating is removed from the support on 
which it is deposited. The process is largely used for 
copying engraved plates for printing purposes. The plate 

221 


Electricity 

is first rubbed over with a very weak solution of beeswax 
in turpentine, to prevent the deposit from adhering to it, 
and it is then placed in a copperplating vat and given a 
good thick coating. The coating is then stripped off, and 
in this w r ay a reversed copy of the plate is obtained. This 
copy is then replaced in the vat, and a coating of copper 
deposited upon it, and this coating, when stripped off, forms 
an exact reproduction of the original, with every detail 
faithfully preserved. An engraved plate may be copied 
also by making from it a mould of plaster or composition. 
The surface of this mould is then rendered conducting by 
sprinkling over it a quantity of plumbago, which is well 
brushed into all the recesses, and a coating of copper 
deposited on it. As the mould was a reversed copy of the 
original, the coating formed upon it is of course an exact 
copy of the plate. If the copy has to be made very quickly 
a preliminary deposit of copper is chemically formed on the 
mould before it is placed in the vat. This is done by 
pouring on to the mould a solution of sulphate of copper, 
and sprinkling iron filings over the surface. The filings 
are then brushed down on to the face of the mould with a 
fine brush, and a chemical reaction takes place, resulting in 
the precipitation of copper from the solution. After the 
filings have been washed away, the mould is placed in the 
vat, and the deposition of copper takes place very rapidly. 

Engraved copperplates are often nickel or steel-plated 
to give their surface greater hardness, so that the printer 
may obtain a larger number of sharp impressions from the 
same plate. Stereotypes also are coated with nickel for a 
similar reason. 

Before the dynamo came into general use all electro¬ 
plating and electrotyping was done with current supplied 
by voltaic cells, and though the dynamo is now used ex¬ 
clusively in large plating works, voltaic cells are still 

222 


Electroplating and Electrotyping 

employed for work on a very small scale. A cell which 
quickly polarizes is quite useless for plating purposes, and 
one giving a constant and ample supply of current is 
required. The Daniell cell, which was described in 
Chapter IV., is used, and so also is the Bunsen cell, which 
consists of a porous pot containing strong nitric acid and a 
carbon rod, placed in an outer stoneware vessel containing 
dilute sulphuric acid and a zinc plate. The drawback to 
this cell is that it gives off very unpleasant fumes. The 
dynamos used for plating work are specially constructed to 
give a large amount of current at very low pressure. 
Continuous current only can be used, for alternating current 
would undo the work as fast as it was done, making the 
article alternately a cathode and an anode. 


223 


CHAPTER XXIII 


INDUSTRIAL ELECTROLYSIS 

The metal copper, as obtained from copper ore, contains 
many impurities of various kinds. For most purposes 
these impurities greatly affect the value of the copper, and 
before the metal can be of much commercial use they must 
be got rid of in some way. In the previous chapter, in 
describing how to copperplate an old spoon, we saw that 
the anode need not consist of pure copper, because in any 
case nothing but the pure metal would be deposited upon 
the spoon. This fact forms the basis of the important 
industry of electrolytic copper refining. The process is 
exactly the same as ordinary copperplating, except that 
the cathode always consists of absolutely pure copper. 
This is generally in the form of a sheet no thicker than 
thin paper, but sometimes a number of suspended wires are 
used instead. A solution of copper sulphate is used as 
usual for the electrolyte, and the anode is a thick cast plate 
of the impure copper. The result of passing a current 
through the solution is that copper is taken from the anode 
and carried to the cathode, the impurities falling to the 
bottom of the vat and accumulating as a sort of slime. In 
this way thick slabs of pure copper are obtained, ready to 
be melted down and cast into ingots. 

The impurities in the raw copper vary according to the 
ore from which it is obtained, and sometimes gold and 
silver are found amongst them. When the copper is known 

224 


Industrial Electrolysis 

to contain these metals the deposit at the bottom of the 
refining vats is carefully collected, and from it a consider¬ 
able quantity of gold and silver is recovered. It is 
estimated that about half a million tons of copper are 
refined every year. An immense amount of this pure 
copper is used for electrical purposes, for making conduct¬ 
ing wires and cables, and innumerable parts of electric 
appliances and machinery of all kinds ; in fact it is calculated 
that more than half of the copper produced all over the 
world is used in this way. 

A similar method is employed to obtain the precious 
metals in a pure state, from the substance known as 
“ bullion ”; which consists usually of an intermingling of 
gold, silver, and copper, with perhaps also lead. Just as in 
copper refining, the raw material is used as the anode, and 
a strip of pure gold or silver, according to which metal is 
required, as the cathode. A silver solution is used if 
silver is wanted, and a gold solution if gold is to be 
deposited. 

The metal aluminium has come into general use with 
surprising rapidity, and during the last twenty-five or 
thirty years the amount of this metal produced annually 
has increased from two or three tons to many thousands 
of tons. Aluminium occurs naturally in large quantities, 
in the form of alumina, or oxide of aluminium, but for a 
long time experimenters despaired of ever obtaining the 
pure metal cheaply on a commercial scale. The oxides of 
most metals can be reduced, that is deprived of their oxygen, 
by heating them with carbon ; but aluminium oxide holds 
on to its oxygen with extraordinary tenacity, and absolutely 
refuses to be parted from it in this way. One process 
after another was tried, without success, and cheap 
aluminium seemed to be an impossibility until about 1887, 
when two chemists, Hall, an American, and H^roult, a 
p 225 


Electricity 

Frenchman, discovered a satisfactory solution of the 
problem. These chemists, who were then scarcely out of 
their student days, worked quite independently of one 
another, and it is a remarkable fact that their methods, 
which are practically alike, were discovered at almost the 
same time. The process is an interesting mixture of 
electrolysis and electric heating. An iron crucible con¬ 
taining a mixture of alumina, fluorspar, and cryolite is 
heated. The two last-named substances are quickly fused, 
and the alumina dissolves in the resulting fluid. When 
the mixture has reached the fluid state, electrodes made of 
carbon are dipped into it, and a current is passed through ; 
with the result that oxygen is given off at the anode, and 
metallic aluminium is produced at the cathode, in molten 
drops. This molten metal is heavier than the rest of the 
fluid, and so it falls to the bottom. From here it is drawn 
off at intervals, while fresh alumina is added as required, 
so that the process goes on without interruption. After 
the first fusing of the mixture no further outside heat is 
required, for the heat produced by the passage of the 
current is sufficient to keep the materials in a fluid state. 
Vast quantities of aluminium are produced in this way at 
Niagara Falls, and in Scotland and Switzerland. 

Most of us are familiar with the substance known as 
caustic soda. The chemical name for this is sodium hydrate, 
and its preparation by electrolysis is interesting. Common 
salt is a chemical compound of the metal sodium and the 
greenish coloured, evil smelling gas chlorine, its proper 
name being sodium chloride. A solution of this in water 
is placed in a vat or cell, and a current is sent through it. 
The solution is then split up into chlorine, at the anode, 
and sodium at the cathode. Sodium has a remarkably 
strong liking for water, and as soon as it is set free from 
the chlorine it combines with the water of the solution, and 

226 


Industrial Electrolysis 

a new solution of sodium hydrate is formed. The water 
in this is then got rid of, and solid caustic soda remains. 

Amongst the many purposes for which caustic soda is 
used is the preparation of oxygen and hydrogen. Water, 
to which a little sulphuric acid has been added, is split up 
by a current into oxygen and hydrogen, as we saw in 
Chapter V. This method may be used for the preparation 
of these two gases on a commercial scale, but more usually 
a solution of caustic soda is used as the electrolyte. If the 
oxygen and hydrogen are not to be used at the place where 
they are produced, they are forced under tremendous 
pressure into steel cylinders, and at a lantern lecture these 
cylinders may be seen supplying the gas for the lime-light. 
Although the cylinders are specially made and tested for 
strength, they are covered with a sort of rope netting; so 
that if by any chance one happened to burst, the shattered 
fragments of metal would be caught by the netting, instead 
of dying all over the room and possibly injuring a number 
of people. A large quantity of hydrogen is prepared by 
this process for filling balloons and military air-ships. 


227 


CHAPTER XXIV 


THE RONTGEN RAYS 

In the chapter on electricity in the atmosphere we saw that 
whereas air at ordinary pressure is a bad conductor, its 
conducting power increases rapidly as the pressure is 
lowered. Roughly speaking, if we wish to obtain a spark 
across a gap of i inch in ordinary air, we must have an 
electric pressure of about 50,000 volts. The discharge 
which takes place under these conditions is very violent, 
and it is called a “disruptive” discharge. If however the 
air pressure is gradually lowered, the discharge loses its 
violent character, and the brilliant spark is replaced by a 
soft, luminous glow. 

The changes in the character of the discharge may be 
studied by means of an apparatus known as the “ electric 
egg.” This consists of an egg-shaped bulb of glass, having 
its base connected with an air-pump. Two brass rods 
project into the bulb, one at each end ; the lower rod being 
a fixture, while the upper one is arranged to slide in and 
out, so that the distance between the balls can be varied. 
The outer ends of the rods are connected to an induction 
coil or to a Wimshurst machine. If the distance between 
the balls has to be, say, half an inch, to produce a spark 
with the air at normal pressure, then on slightly reducing 
the pressure by means of the air-pump it is found that a 
spark will pass with the balls an inch or more apart. The 
brilliance of an electric spark is due to the resistance of the 

228 


The Rontgen Rays 

air, and as the pressure decreases the resistance becomes 
smaller, so that the light produced is much less brilliant. 
If the exhaustion is carried still further the discharge 
becomes redder in colour, and spreads out wider and wider 
until it loses all resemblance to a spark, and becomes a 
luminous glow of a purple or violet colour. At first this 
glow seems to fill the whole bulb, but at still higher vacua 
it contracts into layers of definite shape, these layers being 
alternately light and dark. Finally, when the pressure 
becomes equal to about one-millionth of an atmosphere, a 
luminous glow surrounds the cathode or negative rod, 
beyond this is dark space almost filling the bulb, and the 
walls of the bulb between the cathode and the anode 
glow with phosphorescent light. This phosphorescence is 
produced by rays coming from the cathode and passing 
through the dark space, and these rays have been given the 
name of “cathode rays.” 

Many interesting experiments with these rays may be 
performed with tubes permanently exhausted to the proper 
degree. The power of the rays to produce phosphorescence 
is shown in a most striking way with a tube fixed in a 
horizontal position upon a stand, and containing a light 
cross made of aluminium, placed in the path of the rays. 
This is hinged at the base, so that it can be stood up on end 
or thrown down by jerking the tube. Some of the rays 
streaming from the cathode are intercepted by the cross, 
while others pass by it and reach the other end of the tube. 
The result is that a black shadow of'the cross is thrown on 
the glass, sharply contrasted with those parts of the tube 
reached by the rays, and which phosphoresce brilliantly. 
After a little while this brilliance decreases, for the glass 
becomes fatigued, and loses to a considerable extent its 
power of phosphorescing. If now the cross is jerked down, 
the rays reach the portions of the tube before protected by 

229 


Electricity 

the cross, and this glass, being quite fresh, phosphoresces 
with full brilliance. The black cross now suddenly becomes 
brilliantly illuminated, while the tired glass is dark in 
comparison. If the tired glass is allowed to rest for a while 
it partly recovers its phosphorescing powers, but it never 
regains its first brilliance. 

An even more striking experiment may be made with a 
horizontal tube containing a tiny wheel with vanes of mica, 
something like a miniature water-wheel, mounted on glass 
rails. When the discharges are sent through the tube, the 
cathode rays strike against the vanes and cause the little 
wheel to move forward in the direction of the anode. Other 
experiments show that the cathode rays have great heating 
power, and that they are deflected by a magnet held close 
to the tube. 

For a long time the nature of these cathode rays was in 
dispute. German physicists held that they were of the same 
character as ordinary light, while English scientists, headed 
by Sir William Crookes, maintained that they were streams 
of extremely minute particles of matter in a peculiar fourth 
state. That is to say, the matter was not liquid, or solid, or 
gaseous in the ordinary sense, but was ultra-gaseous , and 
Crookes gave it the name of radiant matter. Most of us 
have been taught to look upon the atom as the smallest 
possible division of matter, but recent researches have made 
it clear that the atom itself is divisible. It is believed that 
an atom is made up of very much more minute particles 
called electrons , which are moving about or revolving all the 
time with incredible rapidity. According to Sir Oliver 
Lodge, if we imagine an atom of hydrogen to be as big as 
an ordinary church, then the electrons which constitute it 
will be represented by about 700 grains of sand, 350 being 
positively electrified and 350 negatively electrified. It is not 
yet definitely determined whether these electrons are minute 

230 


The Rontgen Rays 

particles of matter charged with electricity, or whether they 
are actually atoms of electricity. The majority of scientists 
now believe that the cathode rays consist of a stream of 
negative electrons repelled from the cathode at a speed of 
124 miles per second, or not quite of the velocity of 
light. 

In November 1895, Professor Rontgen, a German 
physicist, announced his discovery of certain invisible rays 
which were produced at the same time as the cathode rays, 
and which could penetrate easily solids quite opaque to 
ordinary light. He was experimenting with vacuum tubes, 
and he found that certain rays emerged from the tube. These 
were not cathode rays, because they were able to pass 
through the glass, and were not deflected by a magnet. To 
these strange rays he gave the name of the “ X ,” or unknown 
rays, but they are very frequently referred to by the name 
of their discoverer. 

It was soon found that the Rontgen rays affected an 
ordinary photographic plate wrapped up in black paper so 
as to exclude all ordinary light, and that they passed 
through flesh much more easily than through bone. This 
fact makes it possible to obtain what we may call “ shadow¬ 
graphs ” of the bones through the flesh, and the value of 
this to the medical profession was realized at once. The 
rays also were found to cause certain chemical compounds 
to become luminous. A cardboard screen covered with 
one of these compounds is quite opaque to ordinary light, 
but if it is examined when the Rontgen rays are falling 
upon it, it is seen to be brightly illuminated, and if the 
hand is held between the screen and the rays the bones 
become clearly visible. 

Rontgen rays are produced when the cathode rays fall 
upon, and as it were bombard, an obstacle of some kind. 
Almost any tube producing cathode rays will produce also 

231 



Electricity 

Rontgen rays, but special forms of tube are used when the 
main object is to obtain these latter rays. Fig. 38 shows 
a typical form of simple X-ray tube. This, like all other 
tubes for X-ray work, is exhausted to a rather higher 
vacuum than tubes intended for the production of cathode 
rays only. The cathode C is made of aluminium, and is 
shaped like a saucer, its curvature being arranged so that 
the cathode rays are focused on to the anti-cathode A. 
The focusing as a rule is not done very accurately, for 



although sharper radiographs are obtained when the cathode 
rays converge exactly to a point on the anti-cathode, the 
heating effect at this point is so great that a hole is quickly 
burned. The target, or surface of the anti-cathode, is 
made of some metal having an extremely high melting- 
point, such as platinum, iridium, or tungsten. It has a flat 
surface inclined at an angle of about 45 0 , so that the rays 
emanating from it proceed in the direction shown by the 
dotted lines in the figure. The continuous lines show the 
direction of the cathode rays. The anode is made of 
aluminium, and it is shown at N. It is not necessary to 

232 











The Rontgen Rays 

have a separate anode, and the anti-cathode may be used 
as the anode. In the tube shown in Fig. 38 the anode 
and the anti-cathode are joined by an insulated wire, so 
that they both act as anodes. The tube is made of soda- 
glass, as the X-rays do not pass at all readily through lead- 
glass. 

The penetrating power of the X-rays varies with the 
vacuum of the tube, a low vacuum giving rays of small 
penetration, and a high vacuum rays of great penetration. 
Tubes are called hard or soft according to the degree of 
the vacuum, a hard 
tube having a high 
vacuum and a soft 
tube a low one. It 
should be remem¬ 
bered that the 
terms high and 
low, as applied to 
the vacuum of X- 
ray tubes, are only 
relative, because 
the vacuum must 
be very high to admit of the production of X-rays at all. 
The vacuum becomes higher as the tube is used, and after a 
while it becomes so high that the tube is practically useless, 
for the penetrating power of the rays is then so great that 
sharp contrasts between different substances, such as flesh 
and bone, cannot be obtained, and the resulting radiographs 
are flat and poor. The vacuum of a hard tube may be 
lowered temporarily by gently heating the tube, but this is 
not a very convenient or satisfactory process, and tubes are 
now made with special arrangements for lowering the 
vacuum when necessary. There are several vacuum¬ 
regulating devices, and Fig. 39 is a diagram of the 

233 



By permission of] 


[C. H. F. Muller . 


Fig. 39.—Diagram of Mica Vacuum Regulator 
for X-Ray Tubes. 












Electricity 

“ Standard ” mica regulator used in most of the well-known 
“ Muller ” X-ray tubes. This consists of a small additional 
bulb containing an electrode D carrying a series of mica 
discs. A wire DF is attached to D by means of a hinged 
cap. The vacuum is lowered while the discharges are 
passing through the tube. The wire DF is moved towards 
the cathode terminal B, and kept there for a few seconds. 
Sparks pass between F and B, and the current is now 
passing through the electrode D in the regulator chamber. 
This causes the mica to become heated, so that it gives off 
a small quantity of gas, which passes into the main tube 
and so lowers the vacuum. The wire DF is then moved 
well away from B, and after a few hours’ rest the tube, now 
of normal hardness, is ready for further use. 

We have already referred to the heating of the anti¬ 
cathode caused by the bombardment of the cathode rays. 
Even if these rays are not focused very sharply, the anti¬ 
cathode of an ordinary tube becomes dangerously hot if 
the tube is run continuously for a fairly long period, and 
for hospital and other medical work on an extensive scale 
special tubes with water-cooled anti-cathodes are used. 
These tubes have a small bulb blown in the anti-cathode 
neck. This bulb is filled with water, which passes down a 
tube to the back of the target of the anti-cathode. By this 
arrangement the heat generated in the target is absorbed 
by the water, so that the temperature of the target can 
become only very slightly higher then 212° F., which 
is the temperature of boiling water, and quite a safe 
temperature for the anti-cathode. In some tubes the rise 
in temperature is made slower by the use of broken bits of 
ice in place of water. Fig. 40 shows a Muller water-cooled 
tube, and Fig. 41 explains clearly the parts of an X-ray 
tube and their names. 

An induction coil is generally used to supply the high- 

234 


Fig. 40. —Muller Water-cooled X-Ray Tube. 



By permission of] [C. H. F. Muller. 

Fig. 41.—Diagram showing parts of X-Ray Tube. 


















































Electricity 

tension electricity required for the production of the Ront- 
gen rays. For amateur or experimental purposes a coil 
giving continuous 4-inch or even 3-inch sparks will 
do, but for medical work, in which it is necessary to take 
radiographs with very short exposures, coils giving sparks 
of 10, 12, or more inches in length are employed. An 
electrical influence machine, such as the Wimshurst, may 
be used instead of an induction coil. Very powerful 
machines with several pairs of plates of large diameter, 
and driven by an electric motor, are in regular use for 
X-ray work in the United States, but in this country they 
are used only to a very small extent. A Wimshurst 
machine is particularly suitable for amateur work. If a 
screen is to be used for viewing bones through the flesh a 
fairly large machine is required, but for screen examination 
of such objects as coins in a box, or spectacles in a case, 
and for taking radiographs of these and other similar 
objects, a machine giving a fairly rapid succession of sparks 
as short as 2 inches can be used. Of course the exposure 
required for taking radiographs with a machine as small as 
this are very long, but as the objects are inanimate this 
does not matter very much. 

For amateur X-ray work the arrangement of the 
apparatus is simple. The tube is held in the required 
position by means of a wooden clamp attached to a stand 
in such a way that it is easily adjustable. Insulated wires 
are led from the coil or from the Wimshurst machine to the 
tube, the positive wire being connected to the anode, and 
the negative wire to the cathode. With a small Wimshurst 
machine light brass chains may be used instead of wires, 
and these have the advantage of being easier to manipulate. 
For medical purposes the arrangements are more com¬ 
plicated, and generally a special room is set apart for X-ray 
work. 


236 


The Rontgen Rays 

If the connexions have been made correctly, then on 
starting the coil or the machine the tube lights up. The 
bulb appears to be sharply divided into two parts, the 
part in front of the anti-cathode glowing with a beautiful 
greenish-yellow light, while the part behind the anti¬ 
cathode is dark, except for lighter patches close to the 
anode. The Rontgen rays are now being produced. The 
illumination is not steady like that of an electric lamp, but 
it consists of a series of flickers, which, with powerful 
apparatus, follow one another so rapidly as to give the 
impression of continuity. If the connexions are wrong, so 
that the negative wire goes to the anode instead of to the 
cathode, the bulb is not divided in this way, but has 
patches of light almost all over. As soon as this appearance 
is seen the apparatus must be stopped and the connexions 
reversed, for the tube is quickly damaged by passing the 
discharge through it in the wrong direction. 

Having produced the X-rays, we will suppose that it 
is desired to examine the bones of the hand. For this 
purpose a fluorescent screen is required. This consists of 
a sheet of white cardboard coated usually with crystals of 
barium platino-cyanide. In order to shut out all light but 
that produced by the rays, the cardboard is placed at the 
larger end of a box or bellows shaped like a pyramid. 
This pyramid is brought close to the X-ray tube, with its 
smaller end held close to the eyes, and the hand is placed 
against the outer side of the cardboard sheet. The outline 
of the hand is then seen as a light shadow, and the very 
much blacker shadow of the bones is clearly visible. For 
screen work it is necessary to darken the room almost 
entirely, on account of the feebleness of the illumination of 
the screen. 

If a radiograph of the bones of the hand is to be taken, 
a very sensitive photographic plate is necessary. An 

237 


Electricity 

ordinary extra-rapid plate will do fairly well, but for the 
best work plates made specially for the purpose are used. 
The emulsion of an ordinary photographic plate is only 
partially opaque to the X-rays, so that while some of the 
rays are stopped by it, others pass straight through. The 
silver bromide in the emulsion is affected only by those 
rays which are stopped, so that the energy of the rays 
which pass through the emulsion is wasted. If a plate is 
coated with a very thick film, a larger proportion of the 
rays can be stopped, and many X-ray plates differ from 
photographic plates only in the thickness of the emulsion. 
A thick film however is undesirable because it makes the 
after processes of developing, fixing, and washing very 
prolonged. In the “ Wratten ” X-ray plate the emulsion is 
made highly opaque to the rays in a different and ingenious 
manner. Salts of certain metals have the power of 
stopping the X-rays, and in this plate a metallic salt of this 
kind is contained in the emulsion. The film produced in 
this way stops a far larger proportion of the rays than any 
ordinary film, and consequently the plate is more sensitive 
to the rays, so that shorter exposures can be given. 

X-ray plates are sold usually wrapped up separately in 
light-tight envelopes of black paper, upon which the film 
side of the plate is marked. If there is no such wrapping 
the plate must be placed in a light-tight envelope, with 
its film facing that side of the envelope which has no folds. 
The ordinary photographic double envelopes, the inner one 
of yellow paper and the outer one of black paper, are very 
convenient for this purpose. The plate in its envelope is 
then laid flat on the table, film side upwards, and the 
X-ray tube is clamped in a horizontal position so that the 
anti-cathode is over and pointing towards the plate. The 
hand is laid flat on the envelope, and the coil or machine is 
set working. The exposure required varies so much with 

238 


The Rontgen Rays 

the size of the machine or coil, the distance between the 
tube and the plate, the condition of the tube, and the nature 
of the object, that it is impossible to give any definite 
times, and these have to be found by experiment. The 
hand requires a shorter exposure than any other part of the 
body. If we call the correct exposure for the hand i, then 
the exposures for other parts of the body would be 
approximately 3 for the foot and the elbow, 6 for the 
shoulder, 8 for the thorax, 10 for the spine and the hip, 
and about 12 for the head. The exposures for such objects 
as coins in a box are much less than for the hand. After 
exposure, the plate is developed, fixed, and washed just as 
in ordinary photography. Plate XIV. shows a Rontgen 
ray photograph of a number of fountain pens, British and 
foreign. 

Prolonged exposure to the X-rays gives rise to a 
painful and serious disease known as X-ray dermatitis. 
This danger was not realized by the early experimenters, 
and many of them contracted the disease, with fatal results 
in one or two cases. Operators now take ample pre¬ 
cautions to protect themselves from the rays. The tubes 
are screened by substances opaque to the rays, so that 
these emerge only where they are required, and 
impenetrable gloves or hand-shields, aprons, and face- 
masks made of rubber impregnated with lead-salts are 
worn. 

X-ray work is a most fascinating pursuit, and it can be 
recommended strongly to amateurs interested in electricity. 
There is nothing particularly difficult about it, and complete 
outfits can be obtained at extremely low prices, although it 
is best to get the most powerful Wimshurst machine or 
induction coil that can be afforded. As radiography is 
most likely to be taken up by photographers, it may be 
well to state here that any photographic plates or papers 

239 


Electricity 

left in their usual wrappings in the room in which X-rays 
are being produced are almost certain to be spoiled, and 
they should be placed in a tightly fitting metal box or be 
taken into the next room. It is not necessary for the 
amateur doing only occasional X-ray work with small 
apparatus to take any of the precautions mentioned in the 
previous paragraph, for there is not the slightest danger in 
such work. 





240 


PLATE XIV, 



RONTGEN RAY PHOTOGRAPH OF BRITISH AND FOREIGN FOUNTAIN PENS. TAKEN ON WRATTEN X-RAY PLATE. 











































CHAPTER XXV 


ELECTRICITY IN MEDICINE 

One of the most remarkable things about electricity is the 
immense number of different purposes for which it may be 
used. We have already seen it driving trams and trains, 
lighting and heating our houses, and carrying our messages 
thousands of miles over land and sea, and now we come to its 
use in medical work. In the minds of many people medical 
electricity is associated with absolute quackery. Advertise¬ 
ments of electric belts, rings, and other similar appliances 
have appeared regularly for many years in our newspapers 
and magazines, and constant exposures of the utter worth¬ 
lessness of almost all these appliances have produced the 
impression that medical electricity is nothing but a bare¬ 
faced fraud, while the disgusting exhibitions of so-called 
electric healing which have been given on the music-hall 
stage have greatly deepened this impression. This state 
of things is very unfortunate, because electricity, in the 
hands of competent medical men, is a healing agent of 
wonderful potency. Still another source of prejudice 
against electricity may be found in the fact that electric 
healing is popularly associated with more or less violent 
shocks. On this account nervously-sensitive people shrink 
from the idea of any kind of electrical treatment. As a 
matter of fact electric shocks have no healing value, but on 
the contrary they are frequently harmful, and a very severe 
shock to a sensitive person may cause permanent injury. 

Q 241 


Electricity 

No shocks whatever are given in electric treatment by 
medical men, and indeed in the majority of cases the treat¬ 
ment is unaccompanied by unpleasant sensations of any kind. 

In the previous chapter we spoke of the use of the 
Rontgen or X-rays in examining the various bones of the 
body. By means of the fluorescent screen it is quite easy 
to find and examine fractures and dislocations, and many 
of the diseases of the bones and joints can be seen and 
recognized. Metals are opaque to the X-rays, and so the 
screen shows plainly such objects as needles or bullets 
embedded in the flesh. Sometimes people, especially 
young children, swallow coins and other small metal articles, 
and here again the X-rays will show the exact position of 
the intruder. A particularly valuable application of the 
rays is in the discovering and locating of tiny fragments of 
metal in the eye, for very often it is quite impossible to do 
this by ordinary observation. Most of these fragments are 
of steel or iron, and they are most easily removed by means 
of an electro-magnet. If the fragment is very small a 
powerful magnet is used, one capable of supporting 500 
or 600 lb. ; but if it is fairly large a weaker magnet, 
supporting perhaps 30 lb., must be employed, because 
the forceful and rapid dragging out of a large body might 
seriously damage the eye. 

If the chest is examined by the Rontgen rays the lungs 
are seen as light spaces between the clearly marked ribs, 
and any spot of congestion appears as a darker patch. In 
this way the early stages of consumption may be revealed, 
and in pneumonia and other similar complaints valuable 
information regarding the condition of the lungs can be 
obtained. It is possible also to follow to a considerable extent 
the processes of digestion. X-rays easily pass through ordin¬ 
ary food, but if bismuth oxychloride, which is quite harm¬ 
less, is mixed with the food, the mixture becomes opaque 

242 


Electricity in Medicine 

to the rays, and so its course may be followed on the screen. 
The normal movements of the food are well known, and an 
abnormal halt is probably caused by an obstruction of some 
kind, and thus the X-rays enable the physician to locate 
the obstruction, and to form an opinion of its nature. 

In our chapter on wireless telegraphy we saw that the 
discharge of a Leyden jar takes the form of a number of 
rapid oscillations backwards and forwards. These oscilla¬ 
tions take place at a rate of more than half a million per 
second, but by the use of an apparatus called a “ high fre¬ 
quency transformer ” the rate is increased to more than a 
million per second. Electricity in this state of rapid oscilla¬ 
tion is known as high frequency electricity, and high fre¬ 
quency currents are very valuable for some kinds of medical 
work. The application of these currents is quite painless, and 
but for the strange-looking apparatus the patient probably 
would not know that anything unusual was taking place. 
To some extent the effect maybe said to be not unlike that 
of a powerful tonic. Insomnia and other troubles due to 
disordered nerves are quickly relieved, and even such 
obstinate complaints as neuritis and crippling rheumatism 
have been cured. The treatment is also of great value in 
certain forms of heart trouble. By increasing the strength 
of the high frequency currents the tissues actually may 
be destroyed, and this power is utilized for exterminating 
malignant growths, such as lupus or cancer. 

The heat produced by a current of electricity is made 
use of in cauterizing. The burner is a loop of platinum 
wire, shaped according to the purpose for which it is 
intended, and it is used at a dull red heat. Very tiny 
electric incandescent lamps, fitted in long holders of special 
shape, are largely used for examining the throat and the 
various cavities of the body. 

In the Finsen light treatment electric light is used for 

243 


Electricity 

a very different purpose. The spectrum of white light con¬ 
sists of the colours red, orange, yellow, green, blue, indigo, 
and violet. Just beyond the violet end of the spectrum are 
the ultra-violet rays. Ultra-violet light consists of waves 
of light which are so short as to be quite invisible to the 
eye, and Dr. N. R. Finsen, a Danish physician, made the 
discovery that this light is capable of destroying bacterial 
germs. In the application of ultra-violet rays to medical 
work, artificial light is used in preference to sunlight; for 
though the latter contains ultra-violet light, a great deal of 
it is absorbed in passing through the atmosphere. Besides 
this, the sun sends out an immense amount of radiant heat, 
and this has to be filtered out before the light can be used. 
The usual source of light is the electric arc, and the arc is 
much richer in ultra-violet rays if it is formed between 
electrodes of iron, instead of the usual carbon rods. The 
light, which, in addition to the ultra-violet rays, includes 
the blue, indigo, and violet parts of the spectrum, is passed 
along a tube something like that of a telescope, and is 
focused by means of a double lens, consisting of two 
separate plates of quartz. Glass cannot be used for the 
lens, because it is opaque to the extreme ultra-violet rays. 
A constant stream of water is passed between the two 
plates forming the lens, and this filters out the heat rays, 
which are not wanted. In some forms of Finsen lamp an 
electric spark is used as the source of light, in place of the 
arc. 

The most important application of the Finsen light is 
in the cure of the terribly disfiguring disease called lupus. 
This is a form of tuberculosis of the skin, and it is pro¬ 
duced by the same deadly microbe which, when it attacks 
the lungs, causes consumption. In all but extreme cases 
the Finsen light effects a remarkable cure. A number of 
applications are necessary, each of half an hour or more ; 

244 


Electricity in Medicine 

and after a time the disease begins to disappear, leaving 
soft, normal skin. The exact action of the light rays is a 
disputed point. Finsen himself believed that the ultra¬ 
violet rays attacked and exterminated the microbe, but a 
later theory is that the rays stimulate the tissues to such 
an extent that they are enabled to cure themselves. As 
early as the year 1899 Finsen had employed his light 
treatment in 350 cases of lupus, and out of this number 
only five cases were unsuccessful. 

The ultra-violet rays are said to have a very beneficial 
effect upon the teeth. Experiments carried out in Paris, 
using a mercury vapour lamp as the source of light, show 
that discoloured teeth are whitened and given a pearly 
lustre by these rays, at the same time being sterilized so 
that they do not easily decay. The Rontgen rays are 
used for the treatment of lupus, and more particularly for 
deeper growths, such as tumours and cancers, for which 
the Finsen rays are useless, owing to their lack of penetrat¬ 
ing power. The action of these two kinds of rays appears 
to be similar, but the X-rays are much the more active of 
the two. 

Electricity is often applied to the body through water, 
in the form of the hydro-electric bath, and such baths 
are used in the treatment of different kinds of paralysis. 
Electric currents are used too for conveying drugs into the 
tissues of the body. This is done when it is desired to 
concentrate the drug at some particular point, and it has 
been found that chemicals can be forced into the tissues for 
a considerable distance. 

Dr. Nagelschmidt, a great authority on medical elec¬ 
tricity, has suggested the use of electricity for weight re¬ 
ducing. In the ordinary way superfluous flesh is got rid 
of by a starvation diet coupled with exercise, but in many 
cases excessively stout people are troubled with heart 

245 


Electricity 

disorders and asthma, so that it is almost impossible for 
them to undergo the necessary muscular exertion. By the 
application of electric currents, however, the beneficial 
effects of the gentle exercise may be produced without any 
exertion on the part of the patient, and an hour’s treatment 
is said to result in a decrease in weight of from 200 to 800 
grammes, or roughly 7 to 27 ounces. 


246 


CHAPTER XXVI 


OZONE 

The great difference between the atmospheric conditions 
before and after a thunderstorm must have been noticed 
by everybody. Before the storm the air feels lifeless. It 
does not satisfy us as we draw it into our lungs, and how¬ 
ever deeply we breathe, we feel that something is lacking. 
After the storm the air is delightful to inhale, and it re¬ 
freshes us with every breath. This remarkable trans¬ 
formation is brought about to a very large extent by ozone 
produced by the lightning discharges. 

As far back as 1785 it was noticed that oxygen became 
changed in some way when an electric spark was passed 
through it, and that it acquired a peculiar odour. No 
particular attention was paid to the matter however until 
about 1840, when Schonbein, a famous German chemist, and 
the discoverer of gun-cotton and collodion, became interested 
in it. He gave this strange smelling substance the name 
of “ ozone,” and he published the results of his experiments 
with it in a treatise entitled, “ On the Generation of 
Ozone.” Schonbein showed that ozone could be produced 
by various methods, chemical as well as electrical. For 
instance, if a piece of phosphorus is suspended in a jar of 
air containing also a little water, in such a manner that it 
is partly in the water and partly out of it, the air acquires 
the characteristic smell of ozone, and it is found to have 
gained increased chemical energy, so that it is a more 

247 


Electricity 

powerful oxidizing agent. For a long time the exact 
chemical nature of ozone could not be determined, mainly 
because it was impossible to obtain the substance in 
quantities sufficiently large for extensive experimental 
research, but also on account of its extremely energetic 
properties, which made it very troublesome to examine. 
These difficulties were so great that investigators were in 
doubt as to whether ozone was an element or a compound 
of two or more elements ; but finally it was proved that it 
was simply oxygen in a condensed or concentrated state. 

Apparently ozone is formed by the contraction of 
oxygen, so that from three volumes of oxygen two volumes 
of ozone are produced. In other words, ozone has one and 
a half times the density of oxygen. Ozone has far greater 
oxidizing power than oxygen itself; in fact it is probably 
the most powerful of all oxidizing agents, and herein lies 
its great value. It acts as nature’s disinfectant or sterilizer, 
and plays a very important part in keeping the air pure, 
by destroying injurious organic matter. Bacteria ap¬ 
parently have a most decided objection to dying; at any 
rate they take an extraordinary amount of killing. Ozone 
is more than a match for them however, and under its 
influence they have a short life and probably not a merry 
one. 

Ozone exists naturally in the atmosphere in the open 
country, and more especially at the seaside. It is pro¬ 
duced by lightning discharges, by silent electrical dis¬ 
charges in the atmosphere, by the evaporation of water, 
particularly salt water, by the action of sunlight, and also 
by the action of certain vegetable products upon the air. 
The quantity of ozone in the air is always small, and even 
pure country or sea air contains only one volume of ozone 
in about 700,000 volumes of air. No ozone can be detected 
in the air of large towns, or over unhealthy swamps or 

248 


Ozone 

marshes. The exhilarating effects of country and sea air, 
and the depressing effects of town air, are due to a very 
large extent to the presence or absence of ozone. 

A great proportion of our common ailments are caused 
directly or indirectly by a sort of slow poisoning, produced 
by the impure air in which we live and work. It is popu¬ 
larly supposed that the tainting of the air of rooms in 
which large numbers of people are crowded together is due 
to an excessive amount of carbonic acid gas. This is a 
mistake, for besides bein^ tasteless and odourless, carbonic 
acid gas is practically harmless, except in quantities far 
greater than ever exist even in the worst ventilated rooms. 
The real source of the tainted air is the great amount of 
animal matter thrown off as waste products from the skin 
and lungs, and this tainting is further intensified by the 
absence of motion in the air. Even in an over-crowded 
room the conditions are made much more bearable if the 
air is kept in motion, and in a close room ladies obtain 
relief by the use of their fans. What we require, there¬ 
fore, in order to maintain an agreeable atmosphere under 
all conditions, is some means of keeping the air in gentle 
motion, and at the same time destroying as much as pos¬ 
sible of the animal matter contained in it. Perhaps the 
most interesting and at the same time the most scientific 
method of doing this is by ozone ventilation. 

In the well-known “Ozonair” system of ventilation, 
ozone is generated by high-tension current. Low-tension 
current is taken from the public mains or from accumulators, 
and raised to a very high voltage by passing it through a 
step-up transformer. The secondary terminals of the 
transformer are connected to a special form of condenser, 
consisting of layers of fine metal gauze separated by an 
insulating substance called “ micanite.” The high tension 
between the gauze layers produces a silent electrical dis- 

249 


Electricity 

charge or glow. A small fan worked by an electric motor 
draws the air over the condenser plates, and so a certain 
proportion of the oxygen is ozonized, and is driven out of 
the other side of the apparatus into the room. The amount 
of ozone generated and the amount of air drawn over the 
condenser are regulated carefully, so that the ozonized air 
contains rather less than one volume of ozone in one 
million volumes of air, experiment having shown that this 
is the most suitable strength for breathing. Ozone diluted 
to this degree has a slight odour which is very refreshing, 
and besides diminishing the number of organic germs in 
the air, it neutralizes unpleasant smells, such as arise from 
cooking or stale tobacco smoke. Ozone ventilation is now 
employed successfully in many hotels, steamships, theatres 
and other places of entertainment, municipal and public 
buildings, and factories. 

One of the most interesting examples of ozone ventila¬ 
tion is that of the Central London tube electric railway. 
The installation consists of a separate ozonizing plant at 
every station, except Shepherd’s Bush, which is close to 
the open end of the tunnel. Fig. 42 is a diagram of the 
general arrangement of one of these plants, and it shows 
how the air is purified, ozonized, and sent into the tunnel. 
The generating plant is seen at the top left-hand corner of 
the figure. Air is drawn in as shown by the arrows, and 
by passing through the filter screen F it is freed from dirt 
and smuts, and from most of the injurious gases which 
always are present in town air. The filter screen is kept 
moist by a continual flow of water from jets above it, the 
waste water falling into the trough W. The ozone 
generator is shown at O. Continuous current at about 
500 volts, from the power station, is passed through a 
rotary converter, which turns it into alternating current at 
38<D.volts. This current goes to the transformer T, from 

250 


Ozone 




251 


Fig. 42.—Diagram of Ozonizing Plant, Central London Tube Electric Railway, 














































































































































































































Electricity 

which it emerges at a pressure of 5000 volts, and is supplied 
to the ozone generator. From the generator the strongly 
ozonized air is taken by way of the ozone pipe P, to the 
mixing chamber of the large ventilating fan M, where it is 
mixed with the main air current and then blown down the 
main air trunk. From this trunk it is distributed to various 
conduits, and delivered at the air outlets marked A. 
Altogether the various plants pump more than eighty 
million cubic feet of ozonized air into the tunnels every 
working day. 

In many industries pure air is very essential, especially 
during certain processes. This is the case in brewing, in 
cold storage, and in the manufacture and canning of food 
products ; and in these industries ozone is employed as an 
air purifier, with excellent results. Other industries cannot 
be carried on without the production of very unpleasant 
fumes and smells, which are a nuisance to the workers and 
often also to the people living round about; and here 
again ozone is used to destroy and remove the offending 
odours. It is employed also in the purification of sewage 
and polluted water ; in bleaching delicate fabrics ; in drying 
and seasoning timber; in maturing tobacco, wines and 
spirits, and in many other processes too numerous to 
mention. 


252 


CHAPTER XXVII 


ELECTRIC IGNITION 

The petrol motor, which to-day is busily engaged all over 
the world in driving thousands upon thousands of self- 
propelled vehicles or automobiles, belongs to the important 
class of internal-combustion engines. Combustion means 
the operation of burning, and an internal-combustion engine 
is one in which the motive power is produced by the com¬ 
bustion of a highly explosive mixture of gases. In the 
ordinary petrol motor this mixture consists of petrol and air, 
and it is made by means of a device called a “ carburetter.” 
By suction, a quantity of petrol is forced through a jet with 
a very fine nozzle, so that it is reduced to an extremely fine 
spray. A certain proportion of air is allowed to enter, and 
the mixture passes into the cylinder. Here it is compressed 
by the rising piston so that it becomes more and more 
heated, and at the right point it is ignited. Combustion 
takes place with such rapidity that it takes the form of an 
explosion, and the energy produced in this way drives 
forward the piston, which turns the crank-shaft and so 
communicates motion to the driving-wheels. 

The part played by electricity in this process is confined 
to the ignition of the compressed charge of petrol and air. 
This may be done in two ways ; by means of an accumulator 
and a small induction coil, or by means of a dynamo driven 
by the engine. At one time the first method was employed 
exclusively, but to-day it is used as a rule only for starting 

253 


Electricity 

the car engine, the second or magneto method being used 
when the engine has started up. 

In accumulator ignition the low-tension current from 
the accumulator passes through an induction coil, and is 
thus transformed to high-tension current. This current 
goes through a sparking plug, which is fixed in the head 
of the cylinder. The sparking plug contains two metal 
points separated by a tiny air gap of from about Ato w 
inch. This gap provides the only possible path for the 
high-tension current, so that the latter leaps across it in 
the form of a spark. The spark is arranged to take place 
when the piston is at the top of its stroke, that is, when the 
explosive mixture is at its maximum compression, and the 
heat of the spark ignites the mixture, the resulting explosion 
forcing down the piston with great power. In practice it 
is found better as a rule to cause the spark to pass very 
slightly before the piston reaches the extreme limit of its 
stroke. The reason of this is that the process of igniting 
and exploding the charge occupies an appreciable, though 
of course exceedingly small amount of time. Immediately 
on reaching the top of its stroke the piston begins to 
descend again, and if the spark and the top of the stroke 
coincide in time the explosion does not take place until the 
piston has moved some little distance down the cylinder, 
and so a certain amount of power is lost. By having the 
spark a little in advance of the piston, the explosion occurs 
at the instant when the piston begins to return, and so the 
full force of the explosion is utilized. 

In magneto ignition the current is supplied by a small 
dynamo. This generates alternating current, and it is 
driven by the car engine. The current is at first at low 
pressure, and it has to be transformed to high-tension 
current in order to produce the spark. There are two 
methods of effecting this transformation. One is by turning 

254 


Electric Ignition 

the armature of the dynamo into a sort of induction coil, by 
giving it two separate windings, primary and secondary ; 
so that the dynamo delivers high-tension current directly. 
The other method is to send the low-tension current 
through one or more transformer coils, just as in accumu¬ 
lator ignition. Accumulators can give current only for a 
certain limited period, and they are liable consequently to 
run down at inconvenient times and places. They also 
have the defect of undergoing a slight leakage of current 
even when they are not in use. Magneto ignition has 
neither of these drawbacks, and on account of its superior 
reliability it has come into universal use. 

In the working of quarries and mines of various kinds, 
and also in large engineering undertakings, blasting plays 
a prominent part. Under all conditions blasting is a more 
or less dangerous business, and it has been the cause of 
very many serious accidents to the men engaged in carrying 
it out. Many of these accidents are due to the carelessness 
resulting from long familiarity with the work, but apart 
from this the danger lies principally in uncertainty in 
exploding the charge. Sometimes the explosion occurs 
sooner than expected, so that the men have not time to get 
away to a safe distance. Still more deadly is the delayed 
explosion. After making the necessary arrangements the 
men retire out of danger, and await the explosion. This 
does not take place at the expected time, and after waiting 
a little longer the men conclude that the ignition has failed, 
and return to put matters right. Then the explosion takes 
place, and the men are killed instantly or at least seriously 
injured. Although it is impossible to avoid altogether 
dangers of this nature, the risk can be reduced to the 
minimum by igniting the explosives by electricity. 

Electrical shot firing may be carried out in different 
ways, according to circumstances. The current is supplied 

255 


Electricity 

either by a dynamo or by a battery, and the firing is controlled 
from a switchboard placed at a safe distance from the point 
at which the charge is to be exploded, the connexions being 
made by long insulated wires. The actual ignition is 
effected by a hot spark, as in automobile ignition, or by an 
electric detonator or fuse. Explosives such as dynamite 
cannot be fired by simple ignition, but require to be 
detonated. This is effected by a detonator consisting of a 
small cup-shaped tube, made of ebonite or other similar 
material. The wires conveying the current project into this 
tube, and are connected by a short piece of very fine wire 
having a high resistance. Round this wire is packed a 
small quantity of gun-cotton, and beyond, in a sort of con¬ 
tinuation of the tube, is placed an extremely explosive 
substance called “ fulminate of mercury,” the whole arrange¬ 
ment being surrounded by the dynamite to be fired. When 
all is ready the man at the switchboard manipulates a 
switch, and the current passes to the detonator and forces 
its way through the resistance of the thin connecting wire. 
This wire becomes sufficiently hot to ignite the gun-cotton, 
and so explode the fulminate of mercury. The explosion 
is so violent that the dynamite charge is detonated, and 
the required blasting carried out. Gunpowder and similar 
explosives do not need to be detonated, and so a simple 
fuse is used. Electric fuses are much the same as deton¬ 
ators, except that the tube contains gunpowder instead of 
fulminate of mercury, this powder being ignited through an 
electrically heated wire in the same way. These electrical 
methods do away with the uncertainty of the slow-burning 
fuses formerly employed, which never could be relied upon 
with confidence. 

Enormous quantities of explosives are now used in 
blasting on a large scale, where many tons of hard rock 
have to be removed. One of the most striking blasting 

256 


Electric Ignition 

feats was the blowing up of Flood Island, better known as 
Hell Gate. This was a rocky islet, about 9 acres in 
extent, situated in the East River, New York. It was a 
continual menace to shipping, and after many fine vessels 
had been wrecked upon it the authorities decided that it 
should be removed. The rock was bored and drilled in all 
directions, the work taking more than a year to complete ; 
and over 126 tons of explosives were filled into the borings. 
The exploding was carried out by electricity, and the 
mighty force generated shattered nearly 300,000 cubic 
yards of solid rock. 


R 


257 


CHAPTER XXVIII 


ELECTRO-CULTURE 

About thirty years ago a Swedish scientist, Professor 
Lemstrom, travelled extensively in the Polar regions, and 
he was greatly struck by the development of the Polar 
vegetation. In spite of the lack of good soil, heat, and 
light, he observed that this vegetation came to maturity 
quicker than that of regions having much more favourable 
climates, and that the colours of the flowers were remark¬ 
ably fresh and clear, and their perfumes exceptionally 
strong. This was a surprising state of things, and 
Lemstrom naturally sought a clue to the mystery. He 
knew that peculiar electrical conditions prevailed in these 
high latitudes, as was shown by the wonderful displays of 
the Aurora Borealis, and he came to the conclusion that 
the development of the vegetation was due to small currents 
of electricity continually passing backwards and forwards 
between the atmosphere and the Earth. On his return to 
civilization Lemstrom at once began a series of experiments 
to determine the effect of electricity upon the growth of 
plants, and he succeeded in proving beyond all doubt that 
plants grown under electrical influence flourished more 
abundantly than those grown in the ordinary way. 
Lemstrom’s experiments have been continued by other 
investigators, and striking and conclusive results have been 
obtained. 

The air surrounding the Earth is always charged to 

258 


Electro-culture 

some extent with electricity, which in fine weather is 
usually positive, but changes to negative on the approach 
of wet weather. This electricity is always leaking away to 
the earth more or less rapidly, and on its way it passes 
through the tissues of the vegetation. An exceedingly 
slow but constant discharge therefore is probably taking 
place in the tissues of all plants. Experiments appear to 
indicate that the upper part of a growing plant is negative, 
and the lower part positive, and at any rate it is certain that 
the leaves of a plant give off negative electricity. In dull 
weather this discharge is at its minimum, but under the 
influence of bright sunshine it goes on with full vigour. It 
is not known exactly how this discharge affects the plant, 
but apparently it assists its development in some way, and 
there is no doubt that when the discharge is at its maximum 
the flow of sap is most vigorous. Possibly the electricity 
helps the plant to assimilate its food, by making this more 
readily soluble. 

This being so, a plant requires a regular daily supply of 
uninterrupted sunshine in order to arrive at its highest 
possible state of maturity. In our notoriously variable 
climate there are many days with only short intermittent 
periods of bright sunshine, and many other days without 
any sunshine at all. Now if, on these dull days, we can 
perform at least a part of the work of the sunshine, and 
strengthen to some extent the minute currents passing 
through the tissues of a plant, the development of this 
plant should be accelerated, and this is found to be the 
case. Under electrical influence plants not only arrive at 
maturity quicker, but also in most cases their yield is 
larger and of finer quality. 

Lemstrom used a large influence machine as the source 
of electricity in his experiments in electro-culture. Such 
machines are very suitable for experimental work on a 

259 


Electricity 

small scale, and much valuable work has been done with 
them by Professor Priestly and others; but they have the 
great drawback of being uncertain in working. They are 
quite satisfactory so long as the atmosphere remains dry, 
but in damp weather they are often very erratic, and may 
require hours of patient labour to coax them to start. For 
this reason an induction coil is more suitable for continuous 
work on an extensive scale. 

The most satisfactory apparatus for electro-culture is 
that used in the Lodge-Newman method, designed by Sir 
Oliver Lodge and his son, working in conjunction with 
Mr. Newman. This consists of a large induction coil 
supplied with current from a dynamo driven by a small 
engine, or from the public mains if available. This coil 
is fitted with a spark gap, and the high-tension current goes 
through four or five vacuum valve globes, the invention 
of Sir Oliver Lodge, which permit the current to pass 
through them in one direction only. This is necessary 
because, as we saw in Chapter VIII., two opposite currents 
are induced in the secondary winding of the coil, one at the 
make and the other at the break of the primary circuit. 
Although the condenser fitted in the base of the coil 
suppresses to a great extent the current induced on making 
the circuit, still the current from the coil is not quite 
unidirectional, but it is made so by the vacuum rectifying 
valves. These are arranged to pass only the positive 
current, and this current is led to overhead wires out in the 
field to be electrified. Lemstrom used wires at a height of 
18 inches from the ground, but these were very much in 
the way, and in the Lodge-Newman system the main wires 
are carried on large porcelain insulators fixed at the top of 
poles at a height of about 15 feet. This arrangement 
allows carting and all other agricultural operations to be 
carried on as usual. The poles are set round the field, 

260 


Electro-culture 

about one to the acre, and from these main wires finer 
ones are carried across the field. These wires are placed 
about 30 feet apart, so that the whole field is covered by a 
network of wires. The electricity supplied to the wires is 
at a pressure of about 100,000 volts, and this is constantly 
being discharged into the air above the plants. It then 
passes through the plants, and so reaches the earth. This 
system may be applied also to plants growing in green¬ 
houses, but owing to the confined space, and to the amount 
of metal about, in the shape of hot-water pipes and wires 
for supporting plants such as vines and cucumbers, it is 
difficult to make satisfactory arrangements to produce the 
discharge. 

o 

The results obtained with this apparatus at Evesham, 
in Gloucestershire, by Mr. Newman, have been most 
striking. With wheat, increases of from 20 per cent, to 
nearly 40 per cent, have been obtained, and the electrified 
wheat is of better quality than unelectrified wheat grown at 
the same place, and, apart from electrification, under exactly 
the same conditions. In some instances the electrified 
wheat was as much as 8 inches higher than the 
unelectrified wheat. Mr. Newman believes that by 
electrification land yielding normally from 30 to 40 bushels 
of wheat per acre can be made to yield 50 or even 60 
bushels per acre. With cucumbers under glass increases 
of 17 per cent, have been obtained, and in the case of 
strawberries, increases of 36 per cent, with old plants, and 
80 per cent, with one-year-old plants. In almost every 
case electrification has produced a marked increase in the 
crop, and in the few cases where there has been a decrease 
the crops were ready earlier than the normal. For instance, 
in one experiment with broad beans a decrease of 15 per 
cent, resulted, but the beans were ready for picking five 
days earlier. In another case a decrease of 11J per cent. 

261 


Electricity 

occurred with strawberries, but the fruit was ready for 
picking some days before the unelectrified fruit, and also 
was much sweeter. In some of the experiments resulting 
in a decrease in the yield it is probable that the electrifica¬ 
tion was overdone, so that the plants were over-stimulated. 
It seems likely that the best results will be obtained only 
by adjusting the intensity and the duration of the electrifi¬ 
cation in accordance with the atmospheric conditions, and 
also with the nature of the crop, for there is no doubt that 
plants vary considerably in their electrical requirements. 
A great deal more experiment is required however to 
enable this to be done with anything like certainty. 

Unlike the farmer, the market gardener has to produce 
one crop after another throughout the year. To make up 
for the absence of sufficient sunshine he has to resort to 
“forcing” in many cases, but unfortunately this process, 
besides being costly, generally results in the production of 
a crop of inferior quality. Evidently the work of the 
market gardener would be greatly facilitated by some 
artificial substitute for sunshine, to keep his plants growing 
properly in dull weather. In 1880, Sir William Siemens, 
knowing that the composition of the light of the electric 
arc was closely similar to that of sunlight, commenced 
experiments with an arc lamp in a large greenhouse. His 
idea was to add to the effects of the solar light by using 
the arc lamp throughout the night. His first efforts were 
unsuccessful, and he discovered that this was due to the 
use of the naked light, which apparently contained rays 
too powerful for the plants. He then passed the light 
through glass, which filtered out the more powerful rays, 
and this arrangement was most successful, the plants 
responding readily to the artificial light. More scientifically 
planned experiments were carried out at the London 
Royal Botanic Gardens in 1907, by Mr. B. H. Thwaite, 

262 


Electro-culture 

and these showed that by using the arc lamp for about five 
hours every night, a great difference between the treated 
plants and other similar plants grown normally could be 
produced in less than a month. Other experiments made 
in the United States with the arc lamp, and also with 
ordinary electric incandescent lamps, gave similar results, 
and it was noticed that the improvement was specially 
marked with cress, lettuce, spinach, and other plants of this 
nature. 

In 1910, Miss E. C. Dudgeon, of Dumfries, commenced 
a series of experiments with the Cooper-Hewitt mercury 
vapour lamp. Two greenhouses were employed, one of 
which was fitted with this lamp. Seeds of various plants 
were sown in small pots, one pot of each kind being placed 
in each house. The temperature and other conditions 
were kept as nearly alike as possible in both houses, and 
in the experimental house the lamp was kept going for 
about five hours every night. In every case the seeds in 
the experimental house germinated several days before 
those in the other house, and the resulting plants were 
healthy and robust. Later experiments carried out by 
Miss Dudgeon with plants were equally successful. 

From these experiments it appears that the electric arc, 
and still more the mercury vapour lamp, are likely to prove 
of great value to the market gardener. As compared with 
the arc lamp, the mercury vapour lamp has the great 
advantage of requiring scarcely any attention, and also it 
uses less current. Unlike the products of ordinary forcing 
by heat, the plants grown under the influence of the 
mercury vapour light are quite sturdy, so that they can be 
planted out with scarcely any “hardening off.” The crop 
yields too are larger, and of better quality. The wonder¬ 
ful effects produced by the Cooper-Hewitt lamp are 
certainly not due to heat, for this lamp emits few heat rays. 

263 


Electricity 

The results may be due partly to longer hours worked by 
the plants, but this does not explain the greater accumula¬ 
tion of chlorophyll and stronger development of fibre. 

Most of us are familiar with the yarn about the poultry 
keeper who fitted all his nests with trap-doors, so that when 
a hen laid an egg, the trap-door opened under the weight 
and allowed the egg to fall through into a box lined with 
hay. The hen then looked round, and finding no egg, at 
once set to work to lay another. This in turn dropped, 
another egg was laid, and so on. It is slightly doubtful 
whether the modern hen could be swindled in this bare¬ 
faced manner, but it is certain that she can be deluded into 
working overtime. The scheme is absurdly simple. 
Electric lamps are fitted in the fowl-house, and at sunset 
the light is switched on. The unsuspecting hens, who are 
just thinking about retiring for the night, come to the con¬ 
clusion that the day is not yet over, and so they continue 
to lay. This is not a yarn, but solid fact, and the increase 
in the egg yield obtained in this way by different poultry 
keepers ranges from io per cent, upwards. Indeed, one 
poultry expert claims to have obtained an increase of about 
40 per cent. 

The ease with which a uniform temperature can be 
maintained by electric heating has been utilized in incubator 
hatching of chickens. By means of a specially designed 
electric radiator the incubator is kept at the right tempera¬ 
ture throughout the hatching period. When the chickens 
emerge from the eggs they are transferred to another 
contrivance called a “brooder,” which also is electrically 
heated, the heat being decreased gradually day by day until 
the chicks are sturdy enough to do without it. Even at 
this stage however the chickens do not always escape 
from the clutches of electricity. Some rearers have 
adopted the electric light swindle for the youngsters, 

264 


Electro-culture 

switching on the light after the chickens have had a fair 
amount of slumber, so that they start feeding again. In 
this way the chickens are persuaded to consume more food 
in the twenty-four hours, and the resulting gain in weight 
is said to be considerable. More interesting than this 
scheme is the method of rearing chickens under the 
influence of an electric discharge from wires supplied with 
high-tension current. Comparative tests show that electri¬ 
fied chickens have a smaller mortality and a much greater 
rate of growth than chickens brought up in the ordinary 
way. It even is said that the electrified chickens have 
more kindly dispositions than their unelectrified relatives! 

Possibly the high-tension discharge may turn out to be 
as beneficial to animals as it has been proved to be for 
plants, but so far there is little reliable evidence on this 
point, owing to lack of experimenters. A test carried out 
in the United States with a flock of sheep is worth 
mention. The flock was divided into two parts, one-half 
being placed in a field under ordinary conditions, and the 
other in a field having a system of overhead discharge 
wires, similar to those used in the Lodge-Newman system. 
The final result was that the electrified sheep produced 
more than twice as many lambs as the unelectrified sheep, 
and also a much greater weight of wool. If further experi¬ 
ments confirm this result, the British farmer will do well to 
consider the advisability of electrifying his live-stock. 


265 


CHAPTER XXIX 


SOME RECENT APPLICATIONS OF ELECTRICITY— 
AN ELECTRIC PIPE LOCATOR 

One of the great advantages of living in a town is the 
abundant supply of gas and water. These necessary 
substances are conveyed to us along underground pipes, 
and a large town has miles upon miles of such pipes, 
extending in all directions and forming a most complex 
network. Gas and water companies keep a record of these 
pipes, with the object of finding any pipe quickly when the 
necessity arises ; but in spite of such records pipes are 
often lost, especially where the whole face of the neighbour¬ 
hood has changed since the pipes were laid. The finding 
of a lost pipe by digging is a very troublesome process, and 
even when the pipe is known to be close at hand, it is quite 
surprising how many attempts are frequently necessary 
before it can be located, and its course traced. As may be 
imagined, this is an expensive business, and often it has been 
found cheaper to lay a new length of pipe than to find the 
old one. There is now an electrical method by which pipe 
locating is made comparatively simple, and unless it is very 
exceptionally deep down, a pipe never need be abandoned 
on account of difficulty in tracing it. 

The mechanism of an electric pipe locator is not at all 
complicated, consisting only of an induction coil with 
battery, and a telephone receiver connected to a coil of a 
large number of turns of thin copper wire. If a certain 

266 





Some Recent Applications of Electricity 

section of a pipe is lost, and has to be located, operations 
are commenced from some fitting known to be connected 
with it, and from some other fitting which may or may not 
be connected with the pipe, but which is believed to be so 
connected. The induction coil is set working, and its 
secondary terminals are connected one to each of these 
fittings. If the second fitting is connected with the pipe, 
then the whole length of the pipe between these two points 
is traversed by the high-frequency current. The searcher, 
wearing the head telephone receiver, with the coil hanging 
down from it so as to be close to the ground, walks to and 
fro over the ground beneath which the pipe must lie. 
When he approaches the pipe the current passing through 
the latter induces a similar current in the suspended coil, 
and this produces a sort of buzzing or humming sound in 
the telephone. The nearer he approaches to the pipe the 
louder is the humming, and it reaches its maximum when 
he is standing directly over the pipe. In this way the 
whole course of the pipe can be traced without any digging, 
even when the pipe is 15 or 20 feet down. The absence 
of any sounds in the receiver indicates that the second 
fitting is not on the required pipe line, and other fittings 
have to be tried until one on this line is found. 

An Electric Iceberg Detector 

Amongst the many dangers to which ships crossing the 
Atlantic are exposed is that of collision with icebergs. 
These are lar^e masses of ice which have become detached 
from the mighty ice-fields of the north, and which travel 
slowly and majestically southwards, growing smaller and 
smaller as they pass into warmer seas. Icebergs give no 
warning of their coming, and in foggy weather, which is very 
prevalent in the regions where they are encountered, they 

267 


Electricity 

are extremely difficult to see until they are at dangerously 
close quarters. 

Attempts have been made to detect the proximity of 
icebergs by noting the variations in the temperature of the 
water. We naturally should expect the temperature of the 
water to become lower as we approach a large berg, and 
this is usually the case. On the other hand, it has been 
found that in many instances the temperature near an 
iceberg is quite as high as, and sometimes higher than the 
average temperature of the ocean. For this reason the 
temperature test, taken by itself, is not at all reliable. A 
much more certain test is that of the salinity or saltness of 
the water. Icebergs are formed from fresh water, and as 
they gradually melt during their southward journey the 
fresh water mixes with the sea water. Consequently the 
water around an iceberg is less salt than the water of the 
open ocean. The saltness of water may be determined by 
taking its specific gravity, or by various chemical processes ; 
but while these tests are quite satisfactory when performed 
under laboratory conditions, they cannot be carried out at sea 
with any approach to accuracy. There is however an elec¬ 
trical test which can be applied accurately and continuously. 
The electrical conducting power of water varies greatly with 
the proportion of salt present. If the conductivity of normal 
Atlantic water be taken as 1000, then the conductivity of 
Thames water is 8, and that of distilled water about 
The difference in conductivity between normal ocean water 
and water in the vicinity of an iceberg is therefore very great. 

The apparatus for detecting differences in salinity by 
measuring the conductivity of the water is called a “ salino- 
meter,” and its most perfect form, known as the heat- 
compensated conductivity salinometer, is due to Dr. Myer 
Coplans. Fig. 43 shows a diagram of this interesting 
piece of apparatus, which is most ingeniously devised. Two 

268 


Some Recent Applications of Electricity 



269 


Fig. 43. —Diagram of Heat-compensated Salinometer. 
































































Electricity 

insulated electrodes of copper, with platinum points, are 
suspended in a (J-tube through which the sea water passes 
continuously, as indicated in the diagram. A steady current 
is passed through the column of water between the two 
platinum points, and the conductivity of this column is 
measured continuously by very accurate instruments. 
Variations in the conductivity, indicating corresponding 
variations in the saltness of the water, are thus shown 
immediately; but before these indications can be relied 
upon the instrument must be compensated for temperature, 
because the conductivity of the water increases with a rise, 
and decreases with a fall in temperature. This compensa¬ 
tion is effected by the compound bars of brass and steel 
shown in the vessel at the right of the figure. These bars 
are connected with the wheel and disc from which the 
electrodes are suspended. When the temperature of the 
water rises, the bars contract, and exert a pull upon the 
wheel and disc, so that the electrodes are raised slightly in 
the U-tube. This increases the length of the column of 
water between the platinum points, and so increases the 
resistance, or, what amounts to the same thing, lowers the 
conductivity, in exact proportion to the rise in temperature. 
Similarly, a fall in temperature lowers the electrodes, and 
decreases the resistance by shortening the column of water. 
In this way the conductivity of the water remains constant 
so far as temperature is concerned, and it varies only with 
the saltness of the water. Under ordinary conditions a 
considerable decrease in the salinity of the water indicates 
the existence of ice in the near neighbourhood, but the 
geographical position of the ship has to be taken into 
account. Rivers such as the St. Lawrence pour vast 
quantities of fresh water into the ocean, and the resulting 
decrease in the saltness of the water within a considerable 
radius of the mouth of the river must be allowed for. 

270 















Some Recent Applications of Electricity 


A “ Flying Train ” 

Considerable interest was aroused last year by a model 
of a railway working upon a very remarkable system. This 
was the invention of Mr. Emile Bachelet, and the model 
was brought to London from the United States. The main 
principle upon which the system is based is interesting. 
About 1884, Professor Elihu Thompson, a famous American 
scientist, made the discovery that a plate of copper could be 
attracted or repelled by an electro-magnet. The effects 
took place at the moment when the magnetism was varied 
by suddenly switching the current on or off; the copper 
being repelled when the current was switched on, and 
attracted when it was switched off. Copper is a non¬ 
magnetic substance, and the attraction and repulsion are 
not ordinary magnetic effects, but are due to currents 
induced in the copper plate at the instant of producing or 
destroying the magnetism. The plate is attracted or 
repelled according to whether these induced currents flow in 
the same direction as, or in the opposite direction to, the 
current in the magnet coil. Brass and aluminium plates 
act in the same way as the copper plate, and the effects are 
produced equally well by exciting the magnet with alternat¬ 
ing current, which, by changing its direction, changes the 
magnetism also. Of the two effects, the repulsion is 
much the stronger, especially if the variations in the 
magnetism take place very rapidly; and if a powerful 
and rapidly alternating current is used, the plate is repelled 
so strongly that it remains supported in mid-air above the 
magnet. 

This repulsive effect is utilized in the Bachelet system 
(Plate XV.). There are no rails in the ordinary sense, and 
the track is made up of a continuous series of electro- 

271 


Electricity 

magnets. The car, which is shaped something like a cigar, 
has a floor of aluminium, and contains an iron cylinder, 
and it runs above the line of magnets. Along each side 
of the track is a channel guide rail, and underneath the car 
at each end are fixed two brushes with guide pieces, which 
run in the guide rails. Above the car is a third guide rail, 
and two brushes with guide pieces fixed on the top of the 
car, one at each end, run in this overhead rail. These 
guide rails keep the car in position, and also act as con¬ 
ductors for the current. The repulsive action of the 
electro-magnets upon the aluminium floor raises the car 
clear of the track, and keeps it suspended; and while 
remaining in this mid-air position it is driven, or rather 
pulled forward, by powerful solenoids, which are supplied 
with continuous current. We have referred previously to 
the way in which a solenoid draws into it a core of iron. 
When the car enters a solenoid, the latter exerts a pulling 
influence upon the iron cylinder inside the car, and so the 
car is given a forward movement. This is sufficient to 
carry it along to the next solenoid, which gives it another 
pull, and so the car is drawn forward from one solenoid 
to another to the end of the line. The model referred 
to has only a short track of about 30 feet, with one 
solenoid at each end; but its working shows that the 
pulling power of the solenoids is sufficient to propel the 
car. 

To avoid the necessity of keeping the whole of the 
electro-magnets energized all the time, these are arranged 
in sections, which are energized separately. By means of 
the lower set of brushes working in the track guides, each 
of these sections has alternating current supplied to it as 
the car approaches, and switched off from it when the car 
has passed. The brushes working in the overhead guide 
supply continuous current to each solenoid as the car enters 

272 


PLATE XV, 



BACHELBT “FLYING TRAIN” AND ITS INVENTOR. 

















Some Recent Applications of Electricity 

it, and switch off the current when the car has passed 
through. The speed at which the model car travels is 
quite extraordinary, and the inventor believes that in actual 
practice speeds of more than 300 miles an hour are attain¬ 
able on his system. 


s 


273 


CHAPTER XXX 


ELECTRICITY IN WAR 

One of the most striking features of modern naval warfare 
is the absolute revolution in methods of communication 
brought about by wireless telegraphy. To-day every 
warship has its wireless installation. Our cruiser squadrons 
and destroyer flotillas, ceaselessly patrolling the waters of 
the North Sea, are always in touch with the Admiral of 
the Fleet, and with the Admiralty at Whitehall. In the 
Atlantic, and in the Pacific too, our cruisers, whether 
engaged in hunting down the marauding cruisers of the 
enemy or in searching for merchant ships laden with con¬ 
traband, have their comings and goings directed by wire¬ 
less. Even before the actual declaration of war between 
Great Britain and Germany wireless telegraphy began its 
work. At the conclusion of the great naval review of 
July 1914, the Fleet left Portland to disperse as customary 
for manoeuvre leave, but a wireless message was dispatched 
ordering the Fleet not to disperse. As no state of war 
then existed, this was a precautionary measure, but sub¬ 
sequent events quickly proved how urgently necessary it 
had been to keep the Fleet in battle array. Immediately 
war was declared Great Britain was able to put into the 
North Sea a fleet which hopelessly outnumbered and out¬ 
classed the German battle fleet. 

At the outset Germany had a number of cruisers in the 
Atlantic and the Pacific Oceans. Owing to the vigilance 

274 


Electricity in War 

of our warships these vessels were unable to join the 
German Home Fleet, and they immediately adopted the 
r 61 e of commerce destroyers. In this work they made 
extensive use of wireless telegraphy to ascertain the where¬ 
abouts of British merchant ships, and for a short time they 
played quite a merry game. Prominent among these 
raiders was the Emden . It was really astonishing how 
this cruiser obtained information regarding the sailings of 
British ships. It is said that on one occasion she called up 
by wireless a merchant ship, and inquired if the latter had 
seen anything of a German cruiser. The unsuspecting 
merchantman replied that there was no such thing as a 
German warship in the vicinity. “Oh yes, there is,” 
returned the Emden ; “ I’m it! ” and shortly afterwards she 
appeared on the horizon, to the great discomfiture of the 
British skipper. An interesting account of the escape of a 
British liner from another notorious raider, the Karlsruhe , 
has been given in the Nautical Magazine. The writer 
says : 

“ I have just returned home after a voyage to South 
America in one of the Pacific Steam Navigation Company’s 
cargo boats. When we left Montevideo we heard that 
France and Germany were at war, and that there was 
every possibility of Great Britain sending an ultimatum to 
Germany. We saw several steamers after leaving the 
port, but could get no information, as few of them were 
fitted with wireless and passed at some distance off. When 
about 200 miles east of Rio, our wireless operator over¬ 
heard some conversation between the German cruiser 
Karlsruhe and a German merchant ship at anchor in Rio. 
It was clearly evident that the German merchant ship had 
no special code, as the conversation was carried on in plain 
German language, and our operator, who, by the way, was 
master of several languages, was able to interpret these 

275 


Electricity 

messages without the slightest difficulty. It was then that 
we learned that Great Britain was at war. The German 
cruiser was inquiring from the German merchant ship what 
British vessels were leaving Rio, and asking for any in¬ 
formation which might be of use. We also picked up some 
news of German victories in Belgium, which were given 
out by the German merchant ship. It was clearly evident 
that the Karlsruhe had information about our ship, and 
expected us to be in the position she anticipated, for she 
sent out a signal to us in English, asking us for our latitude 
and longitude. This our operator, under the instructions 
of the captain, declined to give. The German operator 
evidently got furious, as he called us an English ‘swine- 
hound,’ and said, ‘This is a German warship, Karlsruhe ; 
we will you find.’ Undoubtedly he thought he was going 
to strike terror to our hearts, but he made a mistake. 

“ That night we steamed along without lights, and we 
knew from the sound of the wireless signals that were 
being flashed out from the German ship that we were 
getting nearer and nearer to her. Fortunately for us, 
about midnight a thick misty rain set in and we passed the 
German steamer, and so escaped. Our operator said that 
we could not have been more than 8 or io miles away 
when we passed abeam. Undoubtedly our wireless on 
this occasion saved us from the danger from which we 
escaped.” 

Apparently little is known of the end of the Karlsruhe , 
but the Emden met with the fate she richly deserved ; and 
fittingly enough, wireless telegraphy, which had enabled 
her to carry out her marauding exploits, was the means of 
bringing her to her doom. On 9th November 1914 the 
Emden anchored off the Cocos-Keeling Islands, a group 
of coral islets in the Indian Ocean, and landed a party of 
three officers and forty men to cut the cable and destroy 

276 


Electricity in War 

the wireless station. Before the Germans could get to the 
station, a wireless message was sent out stating the 
presence of the enemy warship, and this call was received 
by the Australian cruisers Melbourne and Sydney. These 
vessels, which were then only some 50 miles away, were 
engaged, along with a Japanese cruiser, in escorting trans¬ 
ports. The Sydney at once went off at full speed, caught 
the Emden , and sent her to the bottom after a short but 
sharp engagement. As the Emden fled at sight of the 
Australian warship, the landing party had not time to get 
aboard, and consequently were left behind. They seized 
an old schooner, provisioned her, and set sail, but what 
became of them is not known. 

In land warfare field telegraphs play a very important 
part; indeed it is certain that without them the vast military 
operations of the present war could not be carried on. 
The General Headquarters of our army in France is in 
telegraphic communication not only with neighbouring 
French towns, but also with Paris and London. From 
Headquarters also run wires to every point of the firing- 
line, so that the Headquarters Staff, and through them the 
War Office in London, know exactly what is taking place 
along the whole front. The following extract from a letter 
from an officer, published by The Times, gives a remark¬ 
ably good idea of the work of the signal companies of the 
Royal Engineers. 

“ As the tide of battle turns this way and the other, and 
headquarters are constantly moving, some means have to be 
provided to keep in constant touch with General Head¬ 
quarters during the movement. This emergency is met 
by cable detachments. Each detachment consists of two 
cable waggons, which usually work in conjunction with one 
another, one section laying the line whilst the other remains 
behind to reel up when the line is finished with. A 

277 


Electricity 

division is ordered to move quickly to a more tactical 
position. The end of the cable is connected with the 
permanent line, which communicates to Army Headquarters, 
and the cable detachment moves off at the trot; across 
country, along roads, through villages, and past columns of 
troops, the white and blue badge of the signal service 
clears the way. Behind the waggon rides a horseman, who 
deftly lays the cable in the ditches and hedges out of danger 
from heavy transport and the feet of tramping infantry, 
with the aid of a crookstick. Other horsemen are in the 
rear tying back and making the line safe. On the box of 
the waggon sits a telegraphist, who is constantly in touch 
with headquarters as the cable runs swiftly out. An 
orderly dashes up with an important message ; the waggon 
is stopped, the message dispatched, and on they go again.” 

Wireless telegraphy too has its part to play in land 
war, and for field purposes it has certain advantages over 
telegraphy with wires. Ordinary telegraphic communica¬ 
tion is liable to be interrupted by the cutting of the wire by 
the enemy, or, in spite of every care in laying, by the 
breaking of the wire by passing cavalry or artillery. No 
such trouble can occur with wireless telegraphy, and if it 
becomes necessary to move a wireless station with great 
rapidity, as for instance on an unexpected advance of the 
enemy, it is an advantage to have no wire to bother about. 
The Marconi portable wireless sets for military purposes 
are marvels of compactness and lightness, combined with 
simplicity. They are of two kinds, pack-saddle sets and 
cart sets. The former weigh about 360 lb., this being 
divided amongst four horses. They can be set up in ten 
minutes by five or six men, and require only two men to 
work them. Their guaranteed range is 40 miles, but 
they are capable of transmitting twice this distance or even 
more under favourable conditions. The cart sets can be 

278 



Electricity in War 

set up in twenty minutes by seven or eight men, and they 
have a guaranteed range of from 150 to 200 miles. 

It is obviously very important that wireless military 
messages should not be intercepted and read by the enemy, 
and the method of avoiding danger of this kind adopted 
with the Marconi field stations is ingenious and effective. 
The transmitter and the receiver are arranged to work on 
three different fixed wave-lengths, the change from one to 
another being effected quickly by the movement of a three- 
position switch. By this means the transmitting operator 
sends three or four words on one wave-length, then changes 
to another, transmits a few words on this, changes the wave¬ 
length again, and so on. Each change is accompanied by 
the sending of a code letter which informs the receiving 
operator to which wave-length the transmitter is passing. 
The receiving operator adjusts his switch accordingly, and 
so he hears the whole message without interruption, the 
change from one wave-length to another taking only a small 
fraction of a second. An enemy operator might manage 
to adjust his wave-length so as to hear two or three words, 
but the sudden change of wave-length would throw him out 
of tune, and by the time he had found the new wave-length 
this would have changed again. Thus he would hear at 
most only a few disconnected words at intervals, and he 
would not be able to make head or tail of the message. 
To provide against the possibility of the three wave-lengths 
being measured and prepared for, these fixed lengths them¬ 
selves can be changed, if necessary, many times a day, so 
that the enemy operators would never know beforehand 
which three were to be used. 

Wireless telegraphy was systematically employed in 
land warfare for the first time in the Balkan War, during 
which it proved most useful both to the Allies and to the 
Turks. One of the most interesting features of the war 

279 


Electricity 

was the way in which wireless communication was kept up 
between the beleaguered city of Adrianople and the 
Turkish capital. Some time before war broke out the 
Turkish Government sent a portable Marconi wireless set 
to Adrianople, and this was set up at a little distance from 
the city. When war was declared the apparatus was 
brought inside the city walls and erected upon a small hill. 
Then came the siege. For 153 days Shukri Pasha kept 
the Turkish flag flying, but the stubborn defence was 
broken down in the end through hunger and disease. All 
through these weary days the little wireless set did its duty 
unfalteringly, and by its aid regular communication was 
maintained with the Government station at Ok Meidan, 
just outside Constantinople, 130 miles away. Altogether 
about half a million words were transmitted from Adrianople 
to the Turkish capital. 

The rapid development of aviation during the past few 
years has drawn attention to the necessity for some means 
of communication between the land and airships and 
aeroplanes in flight. At first sight it might appear that 
wireless telegraphy could be used for this purpose without 
any trouble, but experience has shown that there are 
certain difficulties in the way, especially with regard to 
aeroplanes. The chief difficulty with aeroplanes lies in the 
aerial. This must take the form either of a long trailing 
wire or of fixed wires running between the planes and the 
tail. A trailing wire is open to the objection that it is 
liable to get mixed up with the propeller, besides which it 
appears likely to hamper to some slight extent the move¬ 
ments of a small and light machine. A fixed aerial between 
planes and tail avoids these difficulties, but on the other 
hand its wave-length is bound to be inconveniently small. 
The heavy and powerful British military aeroplanes 
apparently use a trailing wire of moderate length, carried 

280 


ELATE XVT 



By permission of 


( b) AEROPLANE FITTED WITH WIRELESS TELEGRAPHY, 









Electricity in War 

in a special manner so as to clear the propeller, but few 
details are available at present. A further trouble with 
aeroplanes lies in the tremendous noise made by the 
engine, which frequently makes it quite impossible to hear 
incoming signals ; and the only way of getting over this 
difficulty appears to be for the operator to wear some sort 
of sound-proof head-gear. Signals have been transmitted 
from an aeroplane in flight up to distances of 40 or 50 miles 
quite successfully, but the reception of signals by aeroplanes 
is not so satisfactory, except for comparatively short dis¬ 
tances. Although few particulars have been published 
regarding the work of the British aeroplanes in France, it 
seems evident that wireless telegraphy is in regular use. 
In addition to their value as scouts, our aeroplanes appear 
to be extremely useful for the direction of heavy artillery 
fire, using wireless to tell the gunners where each shell falls, 
until the exact range is obtained. In the case of airships 
the problem of wireless communication is much simpler. 
A trailing wire presents no difficulties, and on account of 
their great size much more powerful sets of apparatus can 
be carried. The huge German Zeppelin airships have a 
long freely-floating aerial consisting of a wire which can be 
wound in or let out as required, its full length being about 
750 feet. The total weight of the apparatus is nearly 
300 lb., and the transmitting range is said to be from 
about 120 to 200 miles. 

Electricity is used in the navy for a great variety of 
purposes besides telegraphy. Our battleships are lighted 
by electricity, which is generated at a standard pressure of 
220 volts. This current is transformed down for the 
searchlights, and also for the intricate systems of telephone, 
alarm, and firing circuits. The magazines containing the 
deadly cordite are maintained at a constant temperature of 
70° F. by special refrigerating machinery driven by electricity, 

281 


Electricity 

and the numerous fans for ventilating the different parts of 
the ship are also electrically driven. Electric power is used 
for capstans, coaling winches, sounding machines, lifts, 
pumps, whether for drainage, fire extinction, or raising 
fresh water from the tanks, and for the mechanism for 
operating boats and torpedo nets. The mechanism for 
manipulating the great guns and their ammunition is 
hydraulic. Electricity was tried for this purpose on the 
battle cruiser Invincible , but was abandoned in favour of 
hydraulic power. But though electricity is apparently out of 
favour in this department, it takes an extremely important 
share in the work of controlling and firing the guns; its duties 
being such as could not be carried out by hydraulic power. 

The guns are controlled and fired from what is known 
as the fire-control room, which is situated in the interior of 
the ship, quite away from the guns themselves. The 
range-finder, from his perch up in the gigantic mast, 
watches an enemy warship as she looms on the horizon, 
and when she comes within range he estimates her distance 
by means of instruments of wonderful precision. He then 
telephones to the fire-control room, giving this distance, 
and also the enemy’s speed and course. The officer in 
charge of the fire-control room calculates the elevation of 
the gun required for this distance, and decides upon the 
instant at which the gun must be fired. A telephoned 
order goes to the gun-turret, and the guns are brought to 
bear upon the enemy, laid at the required elevation, and 
sighted. At the correct instant the fire-control officer 
switches on an electric current to the gun, which fires a 
small quantity of highly explosive material, and this in 
turn fires the main charge of cordite. The effect of the 
shell is watched intently from the fire-control top, up above 
the range-finder, and if, as is very likely, this first shell 
falls short of, or overshoots the mark, an estimate of the 

282 


Electricity in War 

amount of error is communicated to the fire-control room. 
Due corrections are then made, the gun is laid at a slightly 
different elevation, and this time the shell finds its mark 
with unerring accuracy. 

The range of movement, horizontal and vertical, of 
modern naval guns is so great that it is possible for two 
guns to be in such relative positions that the firing of one 
would damage the other. To guard against a disaster of ' 
this kind fixed stops are used, supplemented by ingenious 
automatic alarms. The alarm begins to sound as soon as 
any gun passes into a position in which it could damage 
another gun, and it goes on sounding until the latter gun 
is moved out of the danger line. 

Since the outbreak of war the subject of submarine 
mines has been brought to our notice in very forcible 
fashion. Contrary to the general impression, the explosive 
submarine mine is not a recent introduction. It is difficult 
to say exactly when mines were first brought into use, but 
at any rate we know that they were employed by Russia 
during the Crimean War, apparently with little success. 
The first really successful use of mines occurred in the 
American Civil War, when the Confederates sank a number 
of vessels by means of them. This practical demonstration 
of their possibilities did not pass unnoticed by European 
nations, and in the Franco-German War we find that mines 
were used for harbour defence by both belligerents. It is 
doubtful whether either nation derived much benefit from 
its mines, and indeed as the war progressed Germany 
found that the principal result of her mining operations was 
to render her harbours difficult and dangerous to her own 
shipping. Much greater success attended the use of mines 
in the Russo-Japanese War, but all previous records shrink 
into insignificance when compared with the destruction 
wrought by mines in the present great conflict. 

283 


Electricity 

Submarine mines may be divided into two classes; 
those for harbour defence, and those for use in the open 
sea. Harbour defence mines are almost invariably electric¬ 
ally controlled ; that is, they are connected with the shore 
by means of a cable, and fired by an electric impulse sent 
along that cable. In one system of control the moment of 
firing is determined entirely by observers on shore, who, 
aided by special optical instruments, are able to tell exactly 
when a vessel is above any particular mine. The actual 
firing is carried out by depressing a key which completes 
an electric circuit, thus sending a current along the cable 
to actuate the exploding mechanism inside the mine. A 
hostile ship therefore would be blown up on arriving at the 
critical position, while a friendly vessel would be allowed 
to pass on in safety. In this system of control there is no 
contact between the vessel and the mine, the latter being 
well submerged or resting on the sea floor, so that the 
harbour is not obstructed in any way. This is a great 
advantage, but against it must be set possible failure of the 
defence at a critical moment owing to thick weather, which 
of course interferes seriously with the careful observation 
of the mine field necessary for accurate timing of the explo¬ 
sions. This difficulty may be surmounted by a contact 
system of firing. In this case the mines are placed so near 
the surface as to make contact with vessels passing over 
them. The observers on shore are informed of the contact 
by means of an electric impulse automatically transmitted 
along the cable, so that they are independent of continuous 
visual observation of the mined area. As in the previous 
system, the observers give the actual firing impulse. The 
drawback to this method is the necessity for special pilotage 
arrangements for friendly ships in order to avoid unneces¬ 
sary striking of the mines, which are liable to have their 
mechanism deranged by constant blows. If the harbour or 

284 


Electricity in War 

channel can be closed entirely to friendly shipping, the 
observers may be dispensed with, their place being taken 
by automatic electric apparatus which fires at once any mine 
struck by a vessel. 

Shore-controlled mines are excellent for harbour 
defence, and a carefully distributed mine-field, backed by 
heavy fort guns, presents to hostile vessels a barrier which 
may be regarded as almost impenetrable. A strong fleet 
might conceivably force its way through, but in so doing it 
would sustain tremendous losses ; and as these losses would 
be quite out of proportion to any probable gains, such an 
attempt is not likely to be made except as a last resort. 

For use in the open sea a different type of mine is 
required. This must be quite self-contained and automatic 
in action, exploding when struck by a passing vessel. The 
exploding mechanism may take different forms. The blow 
given by a ship may be made to withdraw a pin, thus 
releasing a sort of plunger, which, actuated by a powerful 
spring, detonates the charge. A similar result is obtained 
by the use of a suspended weight, in place of plunger and 
spring. Still another form of mine is fired electrically by 
means of a battery, the circuit of which is closed automati¬ 
cally by the percussion. Deep-sea mines may be anchored 
or floating free. Free mines are particularly dangerous on 
account of the impossibility of knowing where they may be 
at any given moment. They are liable to drift for con¬ 
siderable distances, and to pass into neutral seas ; and to 
safeguard neutral shipping international rules require them 
to have some sort of clockwork mechanism which renders 
them harmless after a period of one hour. It is quite 
certain that some, at least, of the German free mines have 
no such mechanism, so that neutral shipping is greatly 
endangered. 

Submarine mines are known as ground mines, or 

285 


Electricity 

buoyant mines, according to whether they rest on the sea 
bottom or float below the surface. Ground mines are 
generally made in the form of a cylinder, buoyant mines 
being usually spherical. The cases are made of steel, and 
buoyancy is given when required by enclosing air spaces. 
Open-sea mines are laid by special vessels, mostly old 
cruisers. The stern of these ships is partly cut away, and 
the mines are run along rails to the stern, and so overboard. 
The explosive employed is generally gun-cotton, fired by 
a detonator, charges up to 500 lb. or more being used, 
according to the depth of submersion and the horizontal 
distance at which the mine is desired to be effective. 
Ground mines can be used only in shallow water, and even 
then they require a heavier charge than mines floating near 
the surface. Mines must not be laid too close together, as 
the explosion of one might damage others. The distance 
apart at which they are placed depends upon the amount 
of charge, 500-lb. mines requiring to be about 300 feet apart 
for safety. 


286 


CHAPTER XXXI 


WHAT IS ELECTRICITY? 

The question which heads this, our final chapter, is one 
which must occur to every one who takes even the most 
casual interest in matters scientific, and it would be very 
satisfactory if we could bring this volume to a conclusion 
by providing a full and complete answer. Unfortunately 
this is impossible. In years to come the tireless labours of 
scientific investigators may lead to a solution of the problem ; 
but, as Professor Fleming puts it: “ The question—What 
is electricity ?—no more admits of a complete and final 
answer to-day than does the question—What is life ? ” 

From the earliest days of electrical science theories of 
electricity have been put forward. The gradual extension 
and development of these theories, and the constant sub¬ 
stitution of one idea for another as experimental data 
increased, provide a fascinating subject for study. To 
cover this ground however, even in outline, would necessi¬ 
tate many chapters, and so it will be better to consider 
only the theory which, with certain reservations in some 
cases, is held by the scientific world of to-day. This is 
known as the electron theory of electricity. 

We have referred already, in Chapter XXIV., to atoms 
and electrons. All matter is believed to be constituted 
of minute particles called “atoms.” These atoms are so 
extremely small that they are quite invisible, being far 
beyond the range of the most powerful microscope ; and 
their diameter has been estimated at somewhere about one 

287 



Electricity 

millionth of a millimetre. Up to a few years ago the atom 
was believed to be quite indivisible, but it has been proved 
beyond doubt that this is not the case. An atom may be 
said to consist of two parts, one much larger than the 
other. The smaller part is negatively electrified, and is 
the same in all atoms ; while the larger part is positively 
electrified, and varies according to the nature of the atom. 
The small negatively electrified portion of the atom consists of 
particles called “ electrons,” and these electrons are believed 
to be indivisible units or atoms of negative electricity. To 
quote Professor Fleming : “ An atom of matter in its neutral 
condition has been assumed to consist of an outer shell or 
envelope of negative electrons associated with some core or 
matrix which has an opposite electrical quality, such that if 
an electron is withdrawn from the atom the latter is left 
positively electrified.” 

The electrons in an atom are not fixed, but move with 
great velocity, in definite orbits. They repel one another, 
and are constantly endeavouring to fly away from the atom, 
but they are held in by the attraction of the positive core. 
So long as nothing occurs to upset the constitution of the 
atom, a state of equilibrium is maintained and the atom is 
electrically neutral; but immediately the atom is broken up 
by the action of an external force of some kind, one or 
more electrons break their bonds and fly away to join some 
other atom. An atom which has lost some of its electrons 
is no longer neutral, but is electro-positive ; and similarly, 
an atom which has gained additional electrons is electro¬ 
negative. Electrons, or atoms of negative electricity, can 
be isolated from atoms of matter, as in the case of the 
stream of electrons proceeding from the cathode of a vacuum 
tube. So far, however, it has been found impossible to 
isolate corresponding atoms of positive electricity. 

From these facts it appears that we must regard 

288 


a 


What is Electricity ? 

positively charged body as possessing a deficiency of 
electrons, and a negatively charged body as possessing an 
excess of electrons. In Chapter I. we spoke of the 
electrification of sealing-wax or glass rods by friction, and 
we saw that according to the nature of the substance used 
as the rubber, the rods were either positively or negatively 
electrified. Apparently, when we rub a glass rod with a 
piece of silk, the surface atoms of each substance are 
disturbed, and a certain number of electrons leave the glass 
atoms, and join the silk atoms. The surface atoms of the 
glass, previously neutral, are now electro-positive through 
the loss of electrons ; and the surface atoms of the silk, 
also previously neutral, are now electro-negative through 
the additional electrons received from the glass atoms. 
As the result we find the glass to be positively, and silk to 
be negatively electrified. On the other hand, if we rub the 
glass with fur, a similar atomic disturbance and consequent 
migration of electrons takes place, but this time the glass 
receives electrons instead of parting with them. In this case 
the glass becomes negatively, and the fur positively electrified. 
Thequestionnow arises, why is the movement of the electrons 
away from the glass in the first instance, and toward it in 
the second? To understand this we may make use of a 
simple analogy. If we place in contact two bodies, one hot 
and the other cold, the hot body gives up some of its heat 
to the cold body ; but if we place in contact with the hot 
body another body which is still hotter, then the hot body 
receives heat instead of parting with it. In a somewhat 
similar manner an atom is able to give some of its electrons 
to another atom which, in comparison with it, is deficient in 
electrons ; and at the same time it is able to receive elec¬ 
trons from another atom which, compared with it, has an 
excess of electrons. Thus we may assume that the glass 
atoms have an excess of electrons as compared with 
t 289 


Electricity 

silk atoms, and a deficiency in electrons as compared with 
fur atoms. 

A current of electricity is believed to be nothing more 
or less than a stream of electrons, set in motion by the 
application of an electro-motive force. We have seen that 
some substances are good conductors of electricity, while 
others are bad conductors or non-conductors. In order to 
produce an electric current, that is a current of electrons, it 
is evidently necessary that the electrons should be free to- 
move. In good conductors, which are mostly metals, it is 
believed that the electrons are able to move from atom to- 
atom without much hindrance, while in a non-conductor 
their movements are hampered to such an extent that inter¬ 
atomic exchange of electrons is almost impossible. Speak- 
on this point, Professor Fleming says : “ There may be (in 
a good conductor) a constant decomposition and recomposi¬ 
tion of atoms taking place, and any given electron so to 
speak flits about, now forming part of one atom and now of 
another, and anon enjoying a free existence. It resembles 
a person visiting from house to house, forming a unit in 
different households, and, in between, being a solitary 
person in the street. In non-conductors, on the other hand, 
the electrons are much restricted in their movements, and 
can be displaced a little way but are pulled back again 
when released.” 

Let us try to see now how an electric current is set up 
in a simple voltaic cell, consisting of a zinc plate and a 
copper plate immersed in dilute acid. First we must 
understand the meaning of the word ion. If we place a 
small quantity of salt in a vessel containing water, the salt 
dissolves, and the water becomes salt, not only at the 
bottom where the salt was placed, but throughout the 
whole vessel. This means that the particles of salt must be 
able to move through the water. Salt is a chemical 

290 


What is Electricity? 

compound of sodium and chlorine, and its molecules 
consist of atoms of both these substances. It is supposed 
that each salt molecule breaks up into two parts, one part 
being a sodium atom, and the other a chlorine atom ; and 
further, that the sodium atom loses an electron, while the 
chlorine atom gains one. These atoms have the power of 
travelling about through the solution, and they are called 
ions , which means “ wanderers.” An ordinary atom is unable 
to wander about in this way, but it gains travelling power 
as soon as it is converted into an ion, by losing electrons if 
it be an atom of a metal, and by gaining electrons if it be 
an atom of a non-metal. 

Returning to the voltaic cell, we may imagine that the 
atoms of the zinc which are immersed in the acid are trying 
to turn themselves into ions, so that they can travel through 
the solution. In order to do this each atom parts with two 
electrons, and these electrons try to attach themselves to 
the next atom. This atom however already has two 
electrons, and so in order to accept the newcomers it must 
pass on its own two. In this way electrons are passed on 
from atom to atom of the zinc, then along the connecting 
wire, and so to the copper plate. The atoms of zinc which 
have lost their electrons thus become ions, with power of 
movement. They leave the zinc plate immediately, and so 
the plate wastes away or dissolves. So we get a constant 
stream of electrons travelling along the wire connecting the 
two plates, and this constitutes an electric current. 

The electron theory gives us also a clear conception of 
magnetism. An electric current flowing along a wire 
produces magnetic effects ; that is, it sets up a field of 
magnetic force. Such a current is a stream of electrons, 
and therefore we conclude that a magnetic field is produced 
by electrons in motion. This being so, we are led to 
suppose that there must be a stream of electrons in a steel 

291 


Electricity 

magnet, and this stream must be constant because the 
magnetic field of such a magnet is permanent. The 
electron stream in a permanent magnet however is not 
quite the same as the electron stream in a wire conveying a 
current. We have stated that the electrons constituting an 
atom move in definite orbits, so that we may picture them 
travelling round the core of the atom as the planets travel 
round the Sun. This movement is continuous in every 
atom of every substance. Apparently we have here the 
necessary conditions for the production of a magnetic field, 
that is, a constant stream of electrons; but one important 
thing is still lacking. In an unmagnetized piece of steel the 
atoms are not arranged symmetrically, so that the orbits of 
their electrons lie some in one plane and some in another. 
Consequently, although the electron stream of each atom 
undoubtedly produces an infinitesimally small magnetic 
field, no magnetic effect that we can detect is produced, 
because the different streams are not working in unison and 
adding together their forces. In fact they are upsetting 
and neutralizing each other s efforts. By stroking the piece 
of steel with a magnet, or by surrounding it by a coil of 
wire conveying a current, the atoms are turned so that their 
electron orbits all lie in the same plane. The electron 
streams now all work in unison, their magnetic effects are 
added together, and we get a strong magnetic field as the 
result of their combined efforts. Any piece of steel or iron 
may be regarded as a potential magnet, requiring only a 
rearrangement of its atoms in order to become an active 
magnet. In Chapter VI. it was stated that other substances 
besides iron and steel show magnetic effects, and this is what 
we should expect, as the electron movement is common to 
all atoms. None of these substances is equal to iron 
and steel in magnetic power, but why this is so is not 
understood. 


292 


What is Electricity ? 

This brings us to the production of an electric current by 
the dynamo. Here we have a coil of wire moving across a 
magnetic field, alternately passing into this field and out of 
it. A magnetic field is produced, as we have just seen, by 
the steady movement of electrons, and we may picture it 
as being a region of the ether disturbed or strained by the 
effect of the moving electrons. When the coil of wire 
passes into the magnetic field, the electrons of its atoms are 
influenced powerfully and set in motion in one direction, so 
producing a current in the coil. As the coil passes away 
from the field, its electrons receive a second impetus, which 
checks their movement and starts them travelling in the 
opposite direction, and another current is produced. The 
coil moves continuously and regularly, passing into and out 
of the magnetic field without interruption ; and so we get a 
current which reverses its direction at regular intervals, that 
is, an alternating current. This current may be made con¬ 
tinuous if desired, as explained in Chapter IX. 

Such, stated briefly and in outline, is the electron theory 
of electricity. It opens up possibilities of the most fascinat¬ 
ing nature ; it gives us a wonderfully clear conception of 
what might be called the inner mechanism of electricity ; and 
it even introduces us to the very atoms of electricity. 
Beyond this, at present, it cannot take us, and the actual 
nature of electricity itself remains an enigma. 


293 



INDEX 


Accumulators, 38, 90. 

Alarms, electric, 120. 

Alternating currents, 71, 75. 

Amber, discovery of, 2. 

Ampere, 33. 

Arc lamp, 93- 
Armature, 68. 

Atlantic cable, 145. 

Atom, 287. 

Aurora borealis, 25. 

Automatic telephone exchange, 165. 
Aviation and “wireless,” 280. 

Bachelet “flying” train, 271. 

Bastian heater, the, 110. 

Battery, voltaic, 33. 

Bell telephone, the, 156. 

Bells and alarms, electric, 116. 

Blasting, 256. 

Bunsen cell, 223. 

Cable-laying, 150. 

Cables, telegraph, 144. 

Cell, voltaic, 29. 

Clocks, electric, 124. 

Coherer, the, 183. 

Commutator, 70. 

Compass, magnetic, 52. 

Condenser, 63. 

Conductors, 6. 

Conduit system, 83. 

Convectors, 109. 

Cookers, electric, no. 

Creed telegraph, 137. 

Crookes, Sir W., 230. 

Current, electric, 30. 

Daniell cell, 31, 223. 

Davy, Sir Humphry, 93. 

Detector, in wireless telegraphy, 188, 198. 
Diamond-making, 113. 

Duplex telegraphy, 139. 

Dussaud cold light, 106. 

Dynamo, 66. 

Edison, Thomas A., 103. 

Electric cookers, 110. 


Electric heating, 109. 

Electric motor, 66. 

Electric lighting, 70, 75, 93. 

Electricity, early discoveries, 1 ; nature of* 
287. 

Electro-culture, 258. 

Electrolysis, 224. 

Electro-magnets, 58. 

Electron, 287. 

Electroplating, 213. 

Electrophorus, the, 11. 

Electrotyping, 213. 

Faraday, 66. 

Finsen light treatment, 243. 

Franklin, Benjamin, 19. 

Frictional electricity, 2. 

Furnace, electric, III. 

Galvani, 27. 

Galvanometer, 59. 

Glass, 4. 

Goldschmidt system, 197. 

Great Eastern , the, 148. 

Half-watt lamp, 105. 

Heating by electricity, 109. 

Hughes printing telegraph, 136. 

Iceberg detector, 267. 

Ignition, electric, 253. 

Incandescent lamps, 103. 

Induction, 9. 

Induction coil, 61. 

Ion, 291. 

Kelvin, Lord, 152. 

Korn’s photo-telegraph, 174. 

Lamps, electric, 93. 

Leclanche cell, 32, 116. 

Lemstrom’s experiments in electro-culture, 
258. 

Lepel system, 196. 

Leyden jar, 15, 181. 

Light, 23. 

Lighting, electric, 75, 93. 



Index 


Lightning, I, 19, 23. 

Lightning conductors, 25. 

Lindsay, wireless experiments, 180. 
Lodge, Sir Oliver, 260. 

Machines for producing static electricity, 9. 
Magnetic poles, 50. 

Magnetism, 44, 56, 291. 

Marconi, 186, 195. 

Medicine, electricity in, 241. 
Mercury-vapour lamp, 99. 

Microphone, 159. 

Mines, submarine, 283. 

Mines, telephones in, 169. 

Mono-railway, 89. 

Morse, telegraph, 130; experiments in 
wireless telegraphy, 180. 

Motor, electric, 66. 

Motor-car, electric, 91. 

Navy, use of wireless, 274; of electricity, 
282. 

Negative electricity, 5. 

Neon lamps, 102. 

Non-conductors, 6. 

Ohm, 33. 

Oil radiator, no. 

Ozone, 23, 247. 

Ozone ventilation, 249. 

Petrol, motor, ignition in, 253. 
Photographophone, the, 173. 

Pile, voltaic, 28. 

Pipe locator, 266. 

Plant culture, electric, 258. 

Polarization, 31. 

Pollak-Virag telegraph, 137. 

Positive electricity, 5. 

Poulsen, Waldemar, 171, 197. 

Poultry, electro-culture of, 264. 

Power stations, 75. 

Preece, wireless experiments, 180. 

Primary and secondary coils, 62. 

Radiator, 109. 


Railways, electric, 87 ; use of wireless, 211. 
Resistance, 33. 

Rontgen rays, 228, 242. 

Searchlights, 98. 

Ships, use of wireless, 206. 

Siphon recorder, the, 252. 

Sparking plug, 154. 

Static electricity, 7. 

Stations, wireless, 204. 

Steinheil telegraph, 130. 

Submarine telegraphy, 144. 

Submarine telephony, 169. 

Surface contact system, 83. 

Telefunken system, 196. 

Telegraph, the, 128, 144, 171, 179, 203. 
Telegraphone, 171. 

Telephone, the, 154, 171, 179, 201. 
Telephone exchange, 160. 

Thermopile, 36. 

Thermostat, 121. 

Thunderstorms, 22, 194. 

Trains, electric, 87 ; the Bachelet, 271. 
Tramways, electric, 78, 83. 

Trolley system, 83. 

Tubes for X-rays, 233. 

Tuning in wireless telegraphy, 191. 
Tungsten lamps, 104. 

Volt, 33. 

Voltaic electricity, 28, 129, 290. 

War, electricity in, 274 ; telegraph in, 277. 
Water, elec’rolysis of, 38. 

Water-power, 81. 

Waves, electric, 181, 191, 199. 

Welding, electric, 114. 

Welsbach lamp, 103. 

Wheatstone and Cooke telegraphs, 130. 
Wimshurst machine, 12. 

Wireless telegraphy and telephony, 179, 
203, 270, 280. 

Wires, telegraph, 141. 

X-rays, 231, 242. 


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